Add solution and test-cases for problem 528

leetcode/501-600/0528.Random-Pick-with-Weight/README.md

@@ -1,28 +1,53 @@
 # [528.Random Pick with Weight][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+You are given a **0-indexed** array of positive integers `w` where `w[i]` describes the **weight** of the `ith` index.
+
+You need to implement the function `pickIndex()`, which **randomly** picks an index in the range `[0, w.length - 1]` (**inclusive**) and returns it. The **probability** of picking an index i is `w[i] / sum(w)`.
+
+- For example, if `w = [1, 3]`, the probability of picking index `0` is `1 / (1 + 3) = 0.25` (i.e., `25%`), and the probability of picking index `1` is `3 / (1 + 3) = 0.75` (i.e., `75%`).
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input
+["Solution","pickIndex"]
+[[[1]],[]]
+Output
+[null,0]
+
+Explanation
+Solution solution = new Solution([1]);
+solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Random Pick with Weight
-```go
 ```
-
+Input
+["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
+[[[1,3]],[],[],[],[],[]]
+Output
+[null,1,1,1,1,0]
+
+Explanation
+Solution solution = new Solution([1, 3]);
+solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4.
+solution.pickIndex(); // return 1
+solution.pickIndex(); // return 1
+solution.pickIndex(); // return 1
+solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4.
+
+Since this is a randomization problem, multiple answers are allowed.
+All of the following outputs can be considered correct:
+[null,1,1,1,1,0]
+[null,1,1,1,1,1]
+[null,1,1,1,0,0]
+[null,1,1,1,0,1]
+[null,1,0,1,0,0]
+......
+and so on.
+```
 
 ## 结语
 

leetcode/501-600/0528.Random-Pick-with-Weight/Solution.go

@@ -1,5 +1,46 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import (
+	"math/rand"
+	"sort"
+	"time"
+)
+
+type Solution528 struct {
+	sum       int
+	prefixSum []int
+
+	r *rand.Rand
+}
+
+func Constructor(w []int) Solution528 {
+	sum := 0
+
+	prefixSum := make([]int, len(w))
+	for i := range w {
+		sum += w[i]
+		prefixSum[i] = sum
+	}
+	seed := rand.New(rand.NewSource(time.Now().UnixNano()))
+	return Solution528{
+		sum:       sum,
+		prefixSum: prefixSum,
+		r:         seed,
+	}
+}
+
+func (this *Solution528) PickIndex() int {
+	ret := this.r.Intn(this.sum)
+	return sort.Search(len(this.prefixSum), func(i int) bool {
+		return this.prefixSum[i] > ret
+	})
+}
+
+func Solution(w []int, n int) []int {
+	c := Constructor(w)
+	ret := make([]int, n)
+	for i := range n {
+		ret[i] = c.PickIndex()
+	}
+	return ret
 }

leetcode/501-600/0528.Random-Pick-with-Weight/Solution_test.go

@@ -10,30 +10,29 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		w      []int
+		n      int
+		expect []int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{1}, 1, []int{0}},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.w, c.n)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.w, c.n)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }