feat(DEVELOP): create hashMap

src/main/java/core/basesyntax/MyHashMap.java

@@ -1,19 +1,111 @@
 package core.basesyntax;
 
 public class MyHashMap<K, V> implements MyMap<K, V> {
+    private static final int DEFAULT_CAPACITY = 16;
+    private static final float LOAD_FACTOR = 0.75f;
+    private static final int RESIZE_MULTIPLIER = 2;
+
+    private int threshold;
+    private int size;
+    private Node<K, V>[] table;
+
+    public MyHashMap() {
+        this.size = 0;
+        this.threshold = (int) (DEFAULT_CAPACITY * LOAD_FACTOR);
+        this.table = new Node[DEFAULT_CAPACITY];
+    }
 
     @Override
     public void put(K key, V value) {
+        if (size >= threshold) {
+            resize();
+        }
+
+        int index = getIndex(key, table.length);
+        Node<K, V> newNode = new Node<>(key, value);
+
+        if (table[index] == null) {
+            table[index] = newNode;
+            size++;
+            return;
+        }
 
+        Node<K, V> currentNode = table[index];
+        while (true) {
+            if ((currentNode.key == null && key == null)
+                    || (currentNode.key != null && currentNode.key.equals(key))) {
+                currentNode.value = value;
+                return;
+            }
+
+            if (currentNode.next == null) {
+                currentNode.next = newNode;
+                size++;
+                return;
+            }
+
+            currentNode = currentNode.next;
+        }
     }
 
     @Override
     public V getValue(K key) {
+        if (table == null) {
+            return null;
+        }
+
+        int index = getIndex(key, table.length);
+        Node<K, V> currentNode = table[index];
+
+        while (currentNode != null) {
+            if ((currentNode.key == null && key == null)
+                    || (currentNode.key != null && currentNode.key.equals(key))) {
+                return currentNode.value;
+            }
+            currentNode = currentNode.next;
+        }
         return null;
     }
 
     @Override
     public int getSize() {
-        return 0;
+        return size;
+    }
+
+    private void resize() {
+        int newCapacity = table.length * RESIZE_MULTIPLIER;
+        Node<K, V>[] newTable = new Node[newCapacity];
+
+        for (Node<K, V> node : table) {
+            while (node != null) {
+                Node<K, V> nextNode = node.next;
+                int newIndex = getIndex(node.key, newCapacity);
+
+                node.next = newTable[newIndex];
+                newTable[newIndex] = node;
+                node = nextNode;
+            }
+        }
+
+        table = newTable;
+        threshold = (int) (newCapacity * LOAD_FACTOR);
+    }
+
+    private int getIndex(K key, int capacity) {
+        if (key == null) {
+            return 0;
+        }
+        return (key.hashCode() & 0x7fffffff) % capacity;
+    }
+
+    private static class Node<K, V> {
+        private final K key;
+        private V value;
+        private Node<K, V> next;
+
+        public Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
     }
 }