Add solution and test-cases for problem 1664

leetcode/1601-1700/1664.Ways-to-Make-a-Fair-Array/README.md

@@ -1,28 +1,46 @@
 # [1664.Ways to Make a Fair Array][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 an integer array `nums`. You can choose **exactly one** index (**0-indexed**) and remove the element. Notice that the index of the elements may change after the removal.
+
+For example, if `nums = [6,1,7,4,1]`:
+
+- Choosing to remove index `1` results in `nums = [6,7,4,1]`.
+- Choosing to remove index `2` results in `nums = [6,1,4,1]`.
+- Choosing to remove index `4` results in `nums = [6,1,7,4]`.
+
+An array is **fair** if the sum of the odd-indexed values equals the sum of the even-indexed values.
+
+Return the **number** of indices that you could choose such that after the removal, `nums` is **fair**.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: nums = [2,1,6,4]
+Output: 1
+Explanation:
+Remove index 0: [1,6,4] -> Even sum: 1 + 4 = 5. Odd sum: 6. Not fair.
+Remove index 1: [2,6,4] -> Even sum: 2 + 4 = 6. Odd sum: 6. Fair.
+Remove index 2: [2,1,4] -> Even sum: 2 + 4 = 6. Odd sum: 1. Not fair.
+Remove index 3: [2,1,6] -> Even sum: 2 + 6 = 8. Odd sum: 1. Not fair.
+There is 1 index that you can remove to make nums fair.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Ways to Make a Fair Array
-```go
 ```
+Input: nums = [1,1,1]
+Output: 3
+Explanation: You can remove any index and the remaining array is fair.
+```
+
+**Example 3:**
 
+```
+Input: nums = [1,2,3]
+Output: 0
+Explanation: You cannot make a fair array after removing any index.
+```
 
 ## 结语
 

leetcode/1601-1700/1664.Ways-to-Make-a-Fair-Array/Solution.go

@@ -1,5 +1,35 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(nums []int) int {
+	l := len(nums)
+	sum := make([][2]int, l)
+	if (l-1)&1 == 0 {
+		sum[l-1][0] += nums[l-1]
+	} else {
+		sum[l-1][1] += nums[l-1]
+	}
+	for i := l - 2; i >= 0; i-- {
+		sum[i] = sum[i+1]
+		if i&1 == 0 {
+			sum[i][0] += nums[i]
+			continue
+		}
+		sum[i][1] += nums[i]
+	}
+	odd, even := 0, 0
+	ans := 0
+	for i := range l - 1 {
+		if odd+sum[i+1][0] == even+sum[i+1][1] {
+			ans++
+		}
+		if i&1 == 1 {
+			odd += nums[i]
+			continue
+		}
+		even += nums[i]
+	}
+	if odd == even {
+		ans++
+	}
+	return ans
 }

leetcode/1601-1700/1664.Ways-to-Make-a-Fair-Array/Solution_test.go

@@ -10,12 +10,12 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		inputs []int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{2, 1, 6, 4}, 1},
+		{"TestCase2", []int{1, 1, 1}, 3},
+		{"TestCase3", []int{1, 2, 3}, 0},
 	}
 
 	//	开始测试
@@ -30,10 +30,10 @@ func TestSolution(t *testing.T) {
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }