From b75922f45d983ab4e3cbc38324b90be6f40260cb Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Tue, 16 Jan 2024 21:44:12 +0900
Subject: [PATCH 01/12] solve: problem-1-1

---
 problem-1-1/problem-1-1.test.js | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/problem-1-1/problem-1-1.test.js b/problem-1-1/problem-1-1.test.js
index 6ab9348..37dc8bc 100644
--- a/problem-1-1/problem-1-1.test.js
+++ b/problem-1-1/problem-1-1.test.js
@@ -1,4 +1,30 @@
 class Bag {
+  #bag = [];
+
+  isEmpty() {
+    return this.#bag.length === 0;
+  }
+
+  add(item) {
+    this.#bag.push(item);
+  }
+
+  size() {
+    return this.#bag.length;
+  }
+
+  [Symbol.iterator]() {
+    let index = 0;
+    const bag = [...this.#bag];
+
+    return {
+      next() {
+        return index < bag.length
+          ? { done: false, value: bag[index++] }
+          : { done: true };
+      },
+    };
+  }
 }
 
 test('백은 비어있는 상태로 생성된다', () => {

From 66bdd23a653a20d8605b44ae418dee970d0f337b Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Tue, 16 Jan 2024 21:44:31 +0900
Subject: [PATCH 02/12] solve: problem-1-2

---
 problem-1-2/problem-1-2.test.js | 45 +++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/problem-1-2/problem-1-2.test.js b/problem-1-2/problem-1-2.test.js
index f2956b6..e76829d 100644
--- a/problem-1-2/problem-1-2.test.js
+++ b/problem-1-2/problem-1-2.test.js
@@ -1,4 +1,49 @@
+class Bag {
+  #bag = [];
+
+  isEmpty() {
+    return this.#bag.length === 0;
+  }
+
+  add(item) {
+    this.#bag.push(item);
+  }
+
+  size() {
+    return this.#bag.length;
+  }
+
+  sum() {
+    const initialValue = 0;
+    return this.#bag.reduce((acc, currentValue) => acc + currentValue, initialValue);
+  }
+
+  average() {
+    return Math.floor(this.sum() / this.size());
+  }
+
+  [Symbol.iterator]() {
+    let index = 0;
+    const bag = [...this.#bag];
+
+    return {
+      next() {
+        return index < bag.length
+          ? { done: false, value: bag[index++] }
+          : { done: true };
+      },
+    };
+  }
+}
+
 const solution = (numbers) => {
+  const bag = new Bag();
+
+  numbers.forEach((number) => {
+    bag.add(number);
+  });
+
+  return bag.average();
 };
 
 test('숫자 배열의 평균을 반환한다', () => {

From 854651514d03b595d119139e8f080c038387af81 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Thu, 18 Jan 2024 16:31:41 +0900
Subject: [PATCH 03/12] solve: problem-2-1

---
 problem-2-1/problem-2-1.test.js | 64 +++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/problem-2-1/problem-2-1.test.js b/problem-2-1/problem-2-1.test.js
index 17412df..0c898b2 100644
--- a/problem-2-1/problem-2-1.test.js
+++ b/problem-2-1/problem-2-1.test.js
@@ -1,4 +1,68 @@
 class Stack {
+  #capacity;
+
+  #numberOfItem;
+
+  #items;
+
+  constructor(capacity) {
+    this.#capacity = capacity;
+    this.#numberOfItem = 0;
+    this.#items = new Array(capacity);
+  }
+
+  push(item) {
+    // Last In, First Out = LIFO
+    // todo: 아이템을 추가할 때 더 이상 추가할 수 없다면 배열의 크기를 2배로 늘리기
+    if (this.isFull()) {
+      this.#capacity = this.#capacity * 2;
+    }
+
+    this.#items[this.#numberOfItem] = item;
+    this.#numberOfItem += 1;
+  }
+
+  pop() {
+    if (this.isEmpty()) {
+      throw new Error('스택이 비어있습니다.');
+    }
+
+    // todo: 아이템을 제거할 때 아이템의 수가 1 / 4이하라면 배열의 크기를 1/2로 줄이기
+    if (this.isLessThanQuarter()) {
+      this.#capacity = this.#capacity / 2;
+    }
+
+    this.#numberOfItem -= 1;
+    return this.#items[this.#numberOfItem];
+  }
+
+  isLessThanQuarter() {
+    return this.#numberOfItem <= this.#capacity / 4;
+  }
+
+  isEmpty() {
+    return this.#numberOfItem === 0;
+  }
+
+  size() {
+    return this.#numberOfItem;
+  }
+
+  isFull() {
+    return this.#numberOfItem === this.#capacity;
+  }
+
+  [Symbol.iterator]() {
+    let numberOfItem = this.#numberOfItem;
+    const items = this.#items;
+
+    return {
+      next() {
+        numberOfItem = numberOfItem - 1;
+        return numberOfItem >= 0 ? { done: false, value: items[numberOfItem] } : { done: true };
+      },
+    };
+  }
 }
 
 test('스택을 생성하면 비어있다', () => {

From 1f5e0e9f031b0a3e3e73206671628d1001878d96 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Thu, 18 Jan 2024 16:57:51 +0900
Subject: [PATCH 04/12] solve: problem-2-2

---
 problem-2-2/problem-2-2.test.js | 90 +++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/problem-2-2/problem-2-2.test.js b/problem-2-2/problem-2-2.test.js
index dab5212..19d1dc5 100644
--- a/problem-2-2/problem-2-2.test.js
+++ b/problem-2-2/problem-2-2.test.js
@@ -1,4 +1,94 @@
+class Stack {
+  #capacity;
+
+  #numberOfItem;
+
+  #items;
+
+  constructor(capacity) {
+    this.#capacity = capacity;
+    this.#numberOfItem = 0;
+    this.#items = new Array(capacity);
+  }
+
+  push(item) {
+    // Last In, First Out = LIFO
+    // todo: 아이템을 추가할 때 더 이상 추가할 수 없다면 배열의 크기를 2배로 늘리기
+    if (this.isFull()) {
+      this.#capacity = this.#capacity * 2;
+    }
+
+    this.#items[this.#numberOfItem] = item;
+    this.#numberOfItem += 1;
+  }
+
+  pop() {
+    if (this.isEmpty()) {
+      throw new Error('스택이 비어있습니다.');
+    }
+
+    // todo: 아이템을 제거할 때 아이템의 수가 1 / 4이하라면 배열의 크기를 1/2로 줄이기
+    if (this.isLessThanQuarter()) {
+      this.#capacity = this.#capacity / 2;
+    }
+
+    this.#numberOfItem -= 1;
+    return this.#items[this.#numberOfItem];
+  }
+
+  isLessThanQuarter() {
+    return this.#numberOfItem <= this.#capacity / 4;
+  }
+
+  isEmpty() {
+    return this.#numberOfItem === 0;
+  }
+
+  size() {
+    return this.#numberOfItem;
+  }
+
+  isFull() {
+    return this.#numberOfItem === this.#capacity;
+  }
+
+  [Symbol.iterator]() {
+    let numberOfItem = this.#numberOfItem;
+    const items = this.#items;
+
+    return {
+      next() {
+        numberOfItem = numberOfItem - 1;
+        return numberOfItem >= 0 ? { done: false, value: items[numberOfItem] } : { done: true };
+      },
+    };
+  }
+}
+
 const solution = (string) => {
+  const stack = new Stack(string.length);
+  const brackets = { '[': ']', '{': '}', '(': ')' };
+
+  if (string === '') {
+    return stack.isEmpty();
+  }
+
+  for (const char of string) {
+    if (brackets[char]) { // 현재 문자가 열린 괄호라면 = [, {, (
+      stack.push(char);
+    } else { // 현재 문자가 닫힌 괄호라면 = ], }, )
+      if (stack.isEmpty()) { // 현재 스택이 비어 있다면 false
+        return false;
+      }
+
+      const topChar = stack.pop();
+      if (brackets[topChar] !== char) { // 가장 위의 아이템을 꺼내서 짝이 맞는지 비교한다.
+        return false;
+      }
+    }
+  }
+
+  return stack.isEmpty();
 };
 
 test('문자열에 포함된 괄호의 짝이 맞을 때 true를 반환한다', () => {

From 3373ba6ed3019837f6eb2054e39b39c5ab64b863 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Thu, 18 Jan 2024 18:05:27 +0900
Subject: [PATCH 05/12] solve: problem-3-1

---
 problem-3-1/problem-3-1.test.js | 65 +++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/problem-3-1/problem-3-1.test.js b/problem-3-1/problem-3-1.test.js
index 6ae251f..c45775f 100644
--- a/problem-3-1/problem-3-1.test.js
+++ b/problem-3-1/problem-3-1.test.js
@@ -1,4 +1,69 @@
 class Queue {
+  #capacity;
+
+  #numberOfItems;
+
+  #items;
+
+  constructor(capacity) {
+    this.#capacity = capacity;
+    this.#numberOfItems = 0;
+    this.#items = new Array(capacity);
+  }
+
+  enqueue(item) {
+    if (this.isFull()) {
+      throw new Error('용량이 꽉 찼습니다.');
+    }
+
+    this.#items[this.#numberOfItems] = item;
+    this.#numberOfItems += 1;
+  }
+
+  dequeue() {
+    if (this.isEmpty()) {
+      throw new Error('큐가 비어있습니다');
+    }
+
+    // First In, First Out = FIFO
+    const firstItem = this.#items[0];
+
+    // todo : 남은 item 들을 각각 앞으로 옮겨야 한다.
+    for (let index = 1; index < this.#numberOfItems; index += 1) {
+      this.#items[index - 1] = this.#items[index];
+    }
+
+    // item 을 하나 꺼냈으므로 아이템 수 - 1
+    this.#numberOfItems -= 1;
+
+    return firstItem;
+  }
+
+  isEmpty() {
+    return this.#numberOfItems === 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
+  }
+
+  isFull() {
+    return this.#numberOfItems === this.#capacity;
+  }
+
+  [Symbol.iterator]() {
+    let index = 0;
+    const items = this.#items;
+    const numberOfItems = this.#numberOfItems;
+
+    return {
+      next() {
+        return index < numberOfItems
+          ? { done: false, value: items[index++] }
+          : { done: true };
+      },
+    };
+  }
 }
 
 test('큐를 생성하면 비어있다', () => {

From 00d0a954f7c53e1c05907c07d817229b93c614d8 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Thu, 18 Jan 2024 20:39:20 +0900
Subject: [PATCH 06/12] solve: problem-3-2

---
 problem-3-2/problem-3-2.test.js | 93 +++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/problem-3-2/problem-3-2.test.js b/problem-3-2/problem-3-2.test.js
index 21bd836..594fb4e 100644
--- a/problem-3-2/problem-3-2.test.js
+++ b/problem-3-2/problem-3-2.test.js
@@ -1,4 +1,97 @@
+class Queue {
+  #capacity;
+
+  #numberOfItems;
+
+  #items;
+
+  constructor(capacity) {
+    this.#capacity = capacity;
+    this.#numberOfItems = 0;
+    this.#items = new Array(capacity);
+  }
+
+  enqueue(item) {
+    if (this.isFull()) {
+      throw new Error('용량이 꽉 찼습니다.');
+    }
+
+    this.#items[this.#numberOfItems] = item;
+    this.#numberOfItems += 1;
+  }
+
+  dequeue() {
+    if (this.isEmpty()) {
+      throw new Error('큐가 비어있습니다');
+    }
+
+    const firstItem = this.#items[0];
+
+    for (let index = 1; index < this.#numberOfItems; index += 1) {
+      this.#items[index - 1] = this.#items[index];
+    }
+
+    this.#numberOfItems -= 1;
+
+    return firstItem;
+  }
+
+  isEmpty() {
+    return this.#numberOfItems === 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
+  }
+
+  isFull() {
+    return this.#numberOfItems === this.#capacity;
+  }
+
+  [Symbol.iterator]() {
+    let index = 0;
+    const items = this.#items;
+    const numberOfItems = this.#numberOfItems;
+
+    return {
+      next() {
+        return index < numberOfItems
+          ? { done: false, value: items[index++] }
+          : { done: true };
+      },
+    };
+  }
+}
+
+const createNumberArray = (itemCount) => {
+  const resultArray = [];
+
+  for (let index = 1; index <= itemCount; index++) {
+    resultArray.push(index);
+  }
+
+  return resultArray;
+};
+
 const solution = (N, M) => {
+  const numberOfPersons = N;
+  const deathLocation = M;
+
+  const persons = createNumberArray(numberOfPersons);
+
+  const queue = new Queue();
+  persons.forEach((person) => queue.enqueue(person));
+
+  while (queue.size() > 1) {
+    for (let index = 0; index < deathLocation - 1; index += 1) {
+      const personToMove = queue.dequeue();
+      queue.enqueue(personToMove);
+    }
+
+    queue.dequeue();
+  }
+
+  return queue.dequeue();
 };
 
 test('N명의 사람이 있을 때 M번째 사람을 없앨 때 마지막에 죽는 사람의 순서를 반환한다', () => {

From 3ecca82455312628ab579bbbbeddcd3ceaa58358 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Fri, 19 Jan 2024 16:14:55 +0900
Subject: [PATCH 07/12] =?UTF-8?q?refactor:=20Bag=20=EC=9D=84=20=EC=97=B0?=
 =?UTF-8?q?=EA=B2=B0=20=EB=A6=AC=EC=8A=A4=ED=8A=B8=EB=A1=9C=20=EA=B5=AC?=
 =?UTF-8?q?=ED=98=84=ED=95=98=EA=B8=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-1-1/problem-1-1.test.js | 45 +++++++++++++++++++-------
 problem-1-2/problem-1-2.test.js | 56 ++++++++++++++++++++++++---------
 2 files changed, 75 insertions(+), 26 deletions(-)

diff --git a/problem-1-1/problem-1-1.test.js b/problem-1-1/problem-1-1.test.js
index 37dc8bc..dc951f7 100644
--- a/problem-1-1/problem-1-1.test.js
+++ b/problem-1-1/problem-1-1.test.js
@@ -1,27 +1,48 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Bag {
-  #bag = [];
+  #first;
+
+  #numberOfItems;
+
+  constructor() {
+    this.#numberOfItems = 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
+  }
 
   isEmpty() {
-    return this.#bag.length === 0;
+    return this.#numberOfItems === 0;
   }
 
   add(item) {
-    this.#bag.push(item);
-  }
+    const oldFirst = this.#first;
 
-  size() {
-    return this.#bag.length;
+    this.#first = new Node();
+    this.#first.item = item;
+    this.#first.next = oldFirst;
+
+    this.#numberOfItems += 1;
   }
 
   [Symbol.iterator]() {
-    let index = 0;
-    const bag = [...this.#bag];
-
+    let current = this.#first;
     return {
       next() {
-        return index < bag.length
-          ? { done: false, value: bag[index++] }
-          : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }
diff --git a/problem-1-2/problem-1-2.test.js b/problem-1-2/problem-1-2.test.js
index e76829d..d8bba9d 100644
--- a/problem-1-2/problem-1-2.test.js
+++ b/problem-1-2/problem-1-2.test.js
@@ -1,21 +1,46 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Bag {
-  #bag = [];
+  #first;
+
+  #numberOfItems;
+
+  constructor() {
+    this.#numberOfItems = 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
+  }
 
   isEmpty() {
-    return this.#bag.length === 0;
+    return this.#numberOfItems === 0;
   }
 
   add(item) {
-    this.#bag.push(item);
-  }
+    const oldFirst = this.#first;
 
-  size() {
-    return this.#bag.length;
+    this.#first = new Node();
+    this.#first.item = item;
+    this.#first.next = oldFirst;
+
+    this.#numberOfItems += 1;
   }
 
   sum() {
-    const initialValue = 0;
-    return this.#bag.reduce((acc, currentValue) => acc + currentValue, initialValue);
+    let sum = 0;
+    let current = this.#first;
+
+    while (current !== undefined) {
+      sum += current.item;
+      current = current.next;
+    }
+
+    return sum;
   }
 
   average() {
@@ -23,14 +48,17 @@ class Bag {
   }
 
   [Symbol.iterator]() {
-    let index = 0;
-    const bag = [...this.#bag];
-
+    let current = this.#first;
     return {
       next() {
-        return index < bag.length
-          ? { done: false, value: bag[index++] }
-          : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }

From 0a89479d72cfe445ebc4c6ea46ed155403a02aa6 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Fri, 19 Jan 2024 16:16:20 +0900
Subject: [PATCH 08/12] =?UTF-8?q?refactor:=20Stack=20=EC=9D=84=20=EC=97=B0?=
 =?UTF-8?q?=EA=B2=B0=20=EB=A6=AC=EC=8A=A4=ED=8A=B8=EB=A1=9C=20=EA=B5=AC?=
 =?UTF-8?q?=ED=98=84=ED=95=98=EA=B8=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-2-1/problem-2-1.test.js | 75 ++++++++++++++++-----------------
 problem-2-2/problem-2-2.test.js | 75 ++++++++++++++++-----------------
 2 files changed, 72 insertions(+), 78 deletions(-)

diff --git a/problem-2-1/problem-2-1.test.js b/problem-2-1/problem-2-1.test.js
index 0c898b2..d9bb382 100644
--- a/problem-2-1/problem-2-1.test.js
+++ b/problem-2-1/problem-2-1.test.js
@@ -1,65 +1,62 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Stack {
-  #capacity;
+  #first;
 
   #numberOfItem;
 
-  #items;
-
-  constructor(capacity) {
-    this.#capacity = capacity;
+  constructor() {
     this.#numberOfItem = 0;
-    this.#items = new Array(capacity);
+  }
+
+  isEmpty() {
+    return this.#numberOfItem === 0;
+  }
+
+  size() {
+    return this.#numberOfItem;
   }
 
   push(item) {
-    // Last In, First Out = LIFO
-    // todo: 아이템을 추가할 때 더 이상 추가할 수 없다면 배열의 크기를 2배로 늘리기
-    if (this.isFull()) {
-      this.#capacity = this.#capacity * 2;
-    }
+    // todo : 맨 앞에 아이템을 넣는 방식.
+    const oldFirst = this.#first;
+
+    this.#first = new Node();
+    this.#first.item = item;
+    this.#first.next = oldFirst;
 
-    this.#items[this.#numberOfItem] = item;
     this.#numberOfItem += 1;
   }
 
   pop() {
     if (this.isEmpty()) {
-      throw new Error('스택이 비어있습니다.');
-    }
-
-    // todo: 아이템을 제거할 때 아이템의 수가 1 / 4이하라면 배열의 크기를 1/2로 줄이기
-    if (this.isLessThanQuarter()) {
-      this.#capacity = this.#capacity / 2;
+      throw new Error('스택이 비어있습니다');
     }
+    // todo: push 할 때 맨 앞에 가장 최근 아이템이 들어오니까 pop 할 때도 맨 앞에 있는 아이템을 꺼내야 한다.
+    const latestItem = this.#first.item;
+    this.#first = this.#first.next;
 
     this.#numberOfItem -= 1;
-    return this.#items[this.#numberOfItem];
-  }
-
-  isLessThanQuarter() {
-    return this.#numberOfItem <= this.#capacity / 4;
-  }
 
-  isEmpty() {
-    return this.#numberOfItem === 0;
-  }
-
-  size() {
-    return this.#numberOfItem;
-  }
-
-  isFull() {
-    return this.#numberOfItem === this.#capacity;
+    return latestItem;
   }
 
   [Symbol.iterator]() {
-    let numberOfItem = this.#numberOfItem;
-    const items = this.#items;
-
+    let current = this.#first;
     return {
       next() {
-        numberOfItem = numberOfItem - 1;
-        return numberOfItem >= 0 ? { done: false, value: items[numberOfItem] } : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }
diff --git a/problem-2-2/problem-2-2.test.js b/problem-2-2/problem-2-2.test.js
index 19d1dc5..f0db977 100644
--- a/problem-2-2/problem-2-2.test.js
+++ b/problem-2-2/problem-2-2.test.js
@@ -1,65 +1,62 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Stack {
-  #capacity;
+  #first;
 
   #numberOfItem;
 
-  #items;
-
-  constructor(capacity) {
-    this.#capacity = capacity;
+  constructor() {
     this.#numberOfItem = 0;
-    this.#items = new Array(capacity);
+  }
+
+  isEmpty() {
+    return this.#numberOfItem === 0;
+  }
+
+  size() {
+    return this.#numberOfItem;
   }
 
   push(item) {
-    // Last In, First Out = LIFO
-    // todo: 아이템을 추가할 때 더 이상 추가할 수 없다면 배열의 크기를 2배로 늘리기
-    if (this.isFull()) {
-      this.#capacity = this.#capacity * 2;
-    }
+    // todo : 맨 앞에 아이템을 넣는 방식.
+    const oldFirst = this.#first;
+
+    this.#first = new Node();
+    this.#first.item = item;
+    this.#first.next = oldFirst;
 
-    this.#items[this.#numberOfItem] = item;
     this.#numberOfItem += 1;
   }
 
   pop() {
     if (this.isEmpty()) {
-      throw new Error('스택이 비어있습니다.');
-    }
-
-    // todo: 아이템을 제거할 때 아이템의 수가 1 / 4이하라면 배열의 크기를 1/2로 줄이기
-    if (this.isLessThanQuarter()) {
-      this.#capacity = this.#capacity / 2;
+      throw new Error('스택이 비어있습니다');
     }
+    // todo: push 할 때 맨 앞에 가장 최근 아이템이 들어오니까 pop 할 때도 맨 앞에 있는 아이템을 꺼내야 한다.
+    const latestItem = this.#first.item;
+    this.#first = this.#first.next;
 
     this.#numberOfItem -= 1;
-    return this.#items[this.#numberOfItem];
-  }
-
-  isLessThanQuarter() {
-    return this.#numberOfItem <= this.#capacity / 4;
-  }
 
-  isEmpty() {
-    return this.#numberOfItem === 0;
-  }
-
-  size() {
-    return this.#numberOfItem;
-  }
-
-  isFull() {
-    return this.#numberOfItem === this.#capacity;
+    return latestItem;
   }
 
   [Symbol.iterator]() {
-    let numberOfItem = this.#numberOfItem;
-    const items = this.#items;
-
+    let current = this.#first;
     return {
       next() {
-        numberOfItem = numberOfItem - 1;
-        return numberOfItem >= 0 ? { done: false, value: items[numberOfItem] } : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }

From 45eac7b7244dfc05d2617e07d6ddb7842b0aab1f Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Fri, 19 Jan 2024 17:08:54 +0900
Subject: [PATCH 09/12] =?UTF-8?q?refactor:=20Queue=20=EB=A5=BC=20=EC=97=B0?=
 =?UTF-8?q?=EA=B2=B0=20=EB=A6=AC=EC=8A=A4=ED=8A=B8=EB=A1=9C=20=EA=B5=AC?=
 =?UTF-8?q?=ED=98=84=ED=95=98=EA=B8=B0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-3-1/problem-3-1.test.js | 72 +++++++++++++++++----------------
 problem-3-2/problem-3-2.test.js | 69 ++++++++++++++++---------------
 2 files changed, 74 insertions(+), 67 deletions(-)

diff --git a/problem-3-1/problem-3-1.test.js b/problem-3-1/problem-3-1.test.js
index c45775f..8960458 100644
--- a/problem-3-1/problem-3-1.test.js
+++ b/problem-3-1/problem-3-1.test.js
@@ -1,22 +1,39 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Queue {
-  #capacity;
+  #first;
 
-  #numberOfItems;
+  #last;
 
-  #items;
+  #numberOfItems;
 
-  constructor(capacity) {
-    this.#capacity = capacity;
+  constructor() {
     this.#numberOfItems = 0;
-    this.#items = new Array(capacity);
+  }
+
+  isEmpty() {
+    return this.#numberOfItems === 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
   }
 
   enqueue(item) {
-    if (this.isFull()) {
-      throw new Error('용량이 꽉 찼습니다.');
+    const oldLast = this.#last;
+    this.#last = new Node();
+    this.#last.item = item;
+
+    if (this.isEmpty()) {
+      this.#first = this.#last;
+    } else {
+      oldLast.next = this.#last;
     }
 
-    this.#items[this.#numberOfItems] = item;
     this.#numberOfItems += 1;
   }
 
@@ -25,42 +42,27 @@ class Queue {
       throw new Error('큐가 비어있습니다');
     }
 
-    // First In, First Out = FIFO
-    const firstItem = this.#items[0];
+    const firstItem = this.#first.item;
+    this.#first = this.#first.next;
 
-    // todo : 남은 item 들을 각각 앞으로 옮겨야 한다.
-    for (let index = 1; index < this.#numberOfItems; index += 1) {
-      this.#items[index - 1] = this.#items[index];
-    }
-
-    // item 을 하나 꺼냈으므로 아이템 수 - 1
     this.#numberOfItems -= 1;
 
     return firstItem;
   }
 
-  isEmpty() {
-    return this.#numberOfItems === 0;
-  }
-
-  size() {
-    return this.#numberOfItems;
-  }
-
-  isFull() {
-    return this.#numberOfItems === this.#capacity;
-  }
-
   [Symbol.iterator]() {
-    let index = 0;
-    const items = this.#items;
-    const numberOfItems = this.#numberOfItems;
+    let current = this.#first;
 
     return {
       next() {
-        return index < numberOfItems
-          ? { done: false, value: items[index++] }
-          : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }
diff --git a/problem-3-2/problem-3-2.test.js b/problem-3-2/problem-3-2.test.js
index 594fb4e..e5dd6e0 100644
--- a/problem-3-2/problem-3-2.test.js
+++ b/problem-3-2/problem-3-2.test.js
@@ -1,22 +1,39 @@
+class Node {
+  #item;
+
+  #next;
+}
+
 class Queue {
-  #capacity;
+  #first;
 
-  #numberOfItems;
+  #last;
 
-  #items;
+  #numberOfItems;
 
-  constructor(capacity) {
-    this.#capacity = capacity;
+  constructor() {
     this.#numberOfItems = 0;
-    this.#items = new Array(capacity);
+  }
+
+  isEmpty() {
+    return this.#numberOfItems === 0;
+  }
+
+  size() {
+    return this.#numberOfItems;
   }
 
   enqueue(item) {
-    if (this.isFull()) {
-      throw new Error('용량이 꽉 찼습니다.');
+    const oldLast = this.#last;
+    this.#last = new Node();
+    this.#last.item = item;
+
+    if (this.isEmpty()) {
+      this.#first = this.#last;
+    } else {
+      oldLast.next = this.#last;
     }
 
-    this.#items[this.#numberOfItems] = item;
     this.#numberOfItems += 1;
   }
 
@@ -25,39 +42,27 @@ class Queue {
       throw new Error('큐가 비어있습니다');
     }
 
-    const firstItem = this.#items[0];
-
-    for (let index = 1; index < this.#numberOfItems; index += 1) {
-      this.#items[index - 1] = this.#items[index];
-    }
+    const firstItem = this.#first.item;
+    this.#first = this.#first.next;
 
     this.#numberOfItems -= 1;
 
     return firstItem;
   }
 
-  isEmpty() {
-    return this.#numberOfItems === 0;
-  }
-
-  size() {
-    return this.#numberOfItems;
-  }
-
-  isFull() {
-    return this.#numberOfItems === this.#capacity;
-  }
-
   [Symbol.iterator]() {
-    let index = 0;
-    const items = this.#items;
-    const numberOfItems = this.#numberOfItems;
+    let current = this.#first;
 
     return {
       next() {
-        return index < numberOfItems
-          ? { done: false, value: items[index++] }
-          : { done: true };
+        if (current === undefined) {
+          return { done: true };
+        }
+
+        const value = current.item;
+        current = current.next;
+
+        return { done: false, value };
       },
     };
   }

From d1936b3dcee6be43ca53aea8514fe27358971145 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Sat, 20 Jan 2024 17:07:32 +0900
Subject: [PATCH 10/12] =?UTF-8?q?docs:=20README=20=EC=88=98=EC=A0=95=20=20?=
 =?UTF-8?q?-=20=EA=B0=81=20=EC=9E=90=EB=A3=8C=EA=B5=AC=EC=A1=B0=EC=9D=98?=
 =?UTF-8?q?=20API=20=EC=9E=91=EC=84=B1?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-1-1/README.md |  9 ++++++---
 problem-2-1/README.md | 10 +++++++++-
 problem-3-1/README.md | 11 ++++++++---
 3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/problem-1-1/README.md b/problem-1-1/README.md
index 2b698ce..9ae8499 100644
--- a/problem-1-1/README.md
+++ b/problem-1-1/README.md
@@ -2,9 +2,12 @@
 
 1. 백의 정의에 따라서 API를 설계해 주세요.
 
-| 함수 시그니처 | 설명 |
-| ----------- | ----------- |
-| sample(string): number | 문자열을 입력으로 받아 숫자로 변환해서 반환합니다 |
+| 함수 시그니처            | 설명                                                 |
+|--------------------|----------------------------------------------------|
+| `Bag()`              | 백을 생성합니다.                                          |
+| `size(): number`     | 백에 들어있는 아이템 개수를 반환합니다.                             |
+| `isEmpty(): boolean` | 백에 아이템이 없다면 `true`, 아이템이 하나라도 있다면 `false` 를 반환합니다. | 
+| `add(item: any): void` | 백에 아이템을 추가합니다.                                     | 
 
 2. 다음 값들을 백에 추가했을 때 어떻게 되는지 그림으로 그려보세요.
 
diff --git a/problem-2-1/README.md b/problem-2-1/README.md
index 2f9a3e6..af8ce40 100644
--- a/problem-2-1/README.md
+++ b/problem-2-1/README.md
@@ -1,10 +1,18 @@
 # 자료구조와 알고리즘 2주차 과제 - 스택 구현하기
 
 1. 스택의 정의에 따라서 API를 설계해 주세요.
+ - LIFO: Last-In, First-Out (가장 마지막에 담긴 아이템이 가장 먼저 나온다.)
+ - 입력과 출력이 항상 같은 곳에서 일어난다.
+ - 순회할 때는 역순으로 순회한다.
 
 | 함수 시그니처 | 설명 |
 | ----------- | ----------- |
-| sample(string): number | 문자열을 입력으로 받아 숫자로 변환해서 반환합니다 |
+| `Stack()` | 스택을 생성합니다. |
+| `isEmpty(): boolean` | 스택에 아이템이 없다면 `true`, 아이템이 하나라도 있다면 `false` 를 반환합니다. |
+| `size(): number` | 스택에 담긴 아이템의 개수를 반환합니다. |
+| `push(item: any): void` | 스택에 아이템을 추가합니다. |
+| `pop(): item` | 스택에 가장 마지막에 담긴 아이템을 반환합니다. |
+
 
 2. 다음 값들을 스택에 추가했을 때 어떻게 되는지 그림으로 그려보세요. `(-)`은 값을 꺼내는 것을 의미합니다.
 
diff --git a/problem-3-1/README.md b/problem-3-1/README.md
index 4d27b95..e7cd238 100644
--- a/problem-3-1/README.md
+++ b/problem-3-1/README.md
@@ -2,9 +2,14 @@
 
 1. 큐의 정의에 따라서 API를 설계해 주세요.
 
-| 함수 시그니처 | 설명 |
-| ----------- | ----------- |
-| sample(string): number | 문자열을 입력으로 받아 숫자로 변환해서 반환합니다 |
+| 함수 시그니처                    | 설명                                                 |
+|----------------------------|----------------------------------------------------|
+| `Queue()`                  | 큐를 생성합니다.                                          | 
+| `isEmpty(): void`          | 큐에 아이템이 없다면 `true` 를, 아이템이 하나라도 있다면 `false` 를 반환합니다. |
+| `size(): number`           | 큐에 담긴 아이템의 개수를 반환합니다.                              | 
+| `enqueue(item: any): void` | 큐에 아이템을 추가합니다.                                     | 
+| `dequeue(): item`          | 큐의 첫 번째 아이템을 꺼냅니다.                                 | 
+
 
 2. 다음 값들을 큐에 추가했을 때 어떻게 되는지 그림으로 그려보세요. `(-)`은 값을 꺼내는 것을 의미합니다.
 

From 4d40e62842d060cae5983dca41559b8975da9a44 Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Sat, 20 Jan 2024 17:46:01 +0900
Subject: [PATCH 11/12] =?UTF-8?q?refactor:=20dequeue=20=EB=A9=94=EC=84=9C?=
 =?UTF-8?q?=EB=93=9C=20=EC=88=98=EC=A0=95=20=20-=20dequeue()=20=EC=8B=A4?=
 =?UTF-8?q?=ED=96=89=20=ED=9B=84=20queue=20=EC=97=90=20=EC=95=84=EC=9D=B4?=
 =?UTF-8?q?=ED=85=9C=EC=9D=B4=20=EB=82=A8=EC=95=84=20=EC=9E=88=EC=A7=80=20?=
 =?UTF-8?q?=EC=95=8A=EB=8B=A4=EB=A9=B4=20#last=20=EB=8A=94=20undefined=20?=
 =?UTF-8?q?=EB=A5=BC=20=EA=B0=80=EB=A6=AC=EC=BC=9C=EC=95=BC=20=ED=95=9C?=
 =?UTF-8?q?=EB=8B=A4.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-3-1/problem-3-1.test.js | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/problem-3-1/problem-3-1.test.js b/problem-3-1/problem-3-1.test.js
index 8960458..e6cccb7 100644
--- a/problem-3-1/problem-3-1.test.js
+++ b/problem-3-1/problem-3-1.test.js
@@ -45,11 +45,24 @@ class Queue {
     const firstItem = this.#first.item;
     this.#first = this.#first.next;
 
+    // todo: 아이템 개수를 먼저 줄인 다음, isEmpty() 를 확인해서 #last 를 undefined 처리한다.
     this.#numberOfItems -= 1;
 
+    if (this.isEmpty()) {
+      this.#last = undefined;
+    }
+
     return firstItem;
   }
 
+  first() {
+    return this.#first;
+  }
+
+  last() {
+    return this.#last;
+  }
+
   [Symbol.iterator]() {
     let current = this.#first;
 
@@ -100,7 +113,22 @@ test('큐에서 요소를 제거하면 개수가 감소한다', () => {
   expect(newSize - oldSize).toEqual(-1);
 });
 
-test('가장 나중에 삽입한게 먼저 나온다', () => {
+test('가장 먼저 삽입한게 먼저 나온다', () => {
+  const queue = new Queue();
+
+  queue.enqueue('D');
+  queue.enqueue('S');
+  queue.enqueue('A');
+
+  expect(queue.dequeue()).toBe('D');
+  expect(queue.dequeue()).toBe('S');
+  expect(queue.dequeue()).toBe('A');
+
+  expect(queue.first()).toBeUndefined();
+  expect(queue.last()).toBeUndefined();
+});
+
+test('아이템을 모두 제거하면 first, last 는 모두 undefined 를 가리켜야 한다.', () => {
   const queue = new Queue();
 
   queue.enqueue('D');
@@ -110,6 +138,9 @@ test('가장 나중에 삽입한게 먼저 나온다', () => {
   expect(queue.dequeue()).toBe('D');
   expect(queue.dequeue()).toBe('S');
   expect(queue.dequeue()).toBe('A');
+
+  expect(queue.first()).toBeUndefined();
+  expect(queue.last()).toBeUndefined();
 });
 
 test('큐이 비어있는데 dequeue을 하면 예외를 던진다', () => {

From 5d4afc23964954f62238af15e6e6cea9c7f4c09d Mon Sep 17 00:00:00 2001
From: whoodongpyo <vvhooping@gmail.com>
Date: Mon, 22 Jan 2024 12:16:53 +0900
Subject: [PATCH 12/12] =?UTF-8?q?refactor:=20=EB=A6=AC=EB=B7=B0=20?=
 =?UTF-8?q?=EB=B0=98=EC=98=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 problem-1-1/problem-1-1.test.js |  4 ++--
 problem-1-2/problem-1-2.test.js |  4 ++--
 problem-2-1/problem-2-1.test.js |  4 ++--
 problem-2-2/problem-2-2.test.js |  4 ++--
 problem-3-1/problem-3-1.test.js |  4 ++--
 problem-3-2/problem-3-2.test.js | 13 ++++++-------
 6 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/problem-1-1/problem-1-1.test.js b/problem-1-1/problem-1-1.test.js
index dc951f7..2d9a596 100644
--- a/problem-1-1/problem-1-1.test.js
+++ b/problem-1-1/problem-1-1.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Bag {
diff --git a/problem-1-2/problem-1-2.test.js b/problem-1-2/problem-1-2.test.js
index d8bba9d..c4c710e 100644
--- a/problem-1-2/problem-1-2.test.js
+++ b/problem-1-2/problem-1-2.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Bag {
diff --git a/problem-2-1/problem-2-1.test.js b/problem-2-1/problem-2-1.test.js
index d9bb382..2393dba 100644
--- a/problem-2-1/problem-2-1.test.js
+++ b/problem-2-1/problem-2-1.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Stack {
diff --git a/problem-2-2/problem-2-2.test.js b/problem-2-2/problem-2-2.test.js
index f0db977..0e5b231 100644
--- a/problem-2-2/problem-2-2.test.js
+++ b/problem-2-2/problem-2-2.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Stack {
diff --git a/problem-3-1/problem-3-1.test.js b/problem-3-1/problem-3-1.test.js
index e6cccb7..3e86be4 100644
--- a/problem-3-1/problem-3-1.test.js
+++ b/problem-3-1/problem-3-1.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Queue {
diff --git a/problem-3-2/problem-3-2.test.js b/problem-3-2/problem-3-2.test.js
index e5dd6e0..8180ade 100644
--- a/problem-3-2/problem-3-2.test.js
+++ b/problem-3-2/problem-3-2.test.js
@@ -1,7 +1,7 @@
 class Node {
-  #item;
+  item;
 
-  #next;
+  next;
 }
 
 class Queue {
@@ -78,14 +78,13 @@ const createNumberArray = (itemCount) => {
   return resultArray;
 };
 
-const solution = (N, M) => {
-  const numberOfPersons = N;
-  const deathLocation = M;
-
+const solution = (numberOfPersons, deathLocation) => {
   const persons = createNumberArray(numberOfPersons);
 
   const queue = new Queue();
-  persons.forEach((person) => queue.enqueue(person));
+  persons.forEach((person) => {
+    queue.enqueue(person);
+  });
 
   while (queue.size() > 1) {
     for (let index = 0; index < deathLocation - 1; index += 1) {