Merge pull request #1168 from 0xff-dev/775

Add solution and test-cases for problem 775

Author: 6boris

leetcode/701-800/0775.Global-and-Local-Inversions/README.md

@@ -1,28 +1,35 @@
 # [775.Global and Local Inversions][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` of length `n` which represents a permutation of all the integers in the range `[0, n - 1]`.
+
+The number of **global inversions** is the number of the different pairs `(i, j)` where:
+
+- `0 <= i < j < n`
+- `nums[i] > nums[j]`
+
+The number of **local inversions** is the number of indices `i` where:
+
+- `0 <= i < n - 1`
+- `nums[i] > nums[i + 1]`
+
+Return `true` if the number of **global inversions** is equal to the number of **local inversions**.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: nums = [1,0,2]
+Output: true
+Explanation: There is 1 global inversion and 1 local inversion.
 ```
 
-## 题意
-> ...
-
-## 题解
+**Example 2:**
 
-### 思路1
-> ...
-Global and Local Inversions
-```go
 ```
-
+Input: nums = [1,2,0]
+Output: false
+Explanation: There are 2 global inversions and 1 local inversion.
+```
 
 ## 结语
 

leetcode/701-800/0775.Global-and-Local-Inversions/Solution.go

@@ -1,5 +1,48 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func merge(nums []int, left, right int) int {
+	mid := (right-left)/2 + left
+	i, j := left, mid+1
+	temp := make([]int, right-left+1)
+	k := 0
+	reverseOrderPairs := 0
+	for ; i <= mid && j <= right; k++ {
+		if nums[i] > nums[j] {
+			reverseOrderPairs += mid - i + 1
+			temp[k] = nums[j]
+			j++
+			continue
+		}
+		temp[k] = nums[i]
+		i++
+	}
+	for ; i <= mid; i, k = i+1, k+1 {
+		temp[k] = nums[i]
+
+	}
+	for ; j <= right; j, k = j+1, k+1 {
+		temp[k] = nums[j]
+	}
+	for ; k > 0; k-- {
+		nums[left+k-1] = temp[k-1]
+	}
+	return reverseOrderPairs
+}
+func mergeSort(nums []int, left, right int) int {
+	if left < right {
+		mid := (right-left)/2 + left
+		return mergeSort(nums, left, mid) + mergeSort(nums, mid+1, right) + merge(nums, left, right)
+	}
+	return 0
+}
+
+func Solution(nums []int) bool {
+	local := 0
+	for i := 0; i < len(nums)-1; i++ {
+		if nums[i] > nums[i+1] {
+			local++
+		}
+	}
+	global := mergeSort(nums, 0, len(nums)-1)
+	return local == global
 }

leetcode/701-800/0775.Global-and-Local-Inversions/Solution_test.go

@@ -10,12 +10,11 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
+		inputs []int
 		expect bool
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{1, 0, 2}, true},
+		{"TestCase2", []int{1, 2, 0}, false},
 	}
 
 	//	开始测试
@@ -30,10 +29,10 @@ 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() {
 }