Merge pull request #1160 from 0xff-dev/2780

Add solution and test-cases for problem 2780

Author: 6boris

leetcode/2701-2800/2780.Minimum-Index-of-a-Valid-Split/README.md

@@ -0,0 +1,54 @@
+# [2780.Minimum Index of a Valid Split][title]
+
+## Description
+An element `x` of an integer array `arr` of length `m` is **dominant** if **more than half** the elements of `arr` have a value of `x`.
+
+You are given a **0-indexed** integer array `nums` of length `n` with one **dominant** element.
+
+You can split `nums` at an index `i` into two arrays `nums[0, ..., i]` and `nums[i + 1, ..., n - 1]`, but the split is only **valid** if:
+
+- `0 <= i < n - 1`
+- `nums[0, ..., i]`, and `nums[i + 1, ..., n - 1]` have the same dominant element.
+
+Here, `nums[i, ..., j]` denotes the subarray of `nums` starting at index `i` and ending at index `j`, both ends being inclusive. Particularly, if `j < i` then `nums[i, ..., j]` denotes an empty subarray.
+
+Return the **minimum** index of a *8valid split**. If no valid split exists, return `-1`.
+
+**Example 1:**
+
+```
+Input: nums = [1,2,2,2]
+Output: 2
+Explanation: We can split the array at index 2 to obtain arrays [1,2,2] and [2]. 
+In array [1,2,2], element 2 is dominant since it occurs twice in the array and 2 * 2 > 3. 
+In array [2], element 2 is dominant since it occurs once in the array and 1 * 2 > 1.
+Both [1,2,2] and [2] have the same dominant element as nums, so this is a valid split. 
+It can be shown that index 2 is the minimum index of a valid split. 
+```
+
+**Example 2:**
+
+```
+Input: nums = [2,1,3,1,1,1,7,1,2,1]
+Output: 4
+Explanation: We can split the array at index 4 to obtain arrays [2,1,3,1,1] and [1,7,1,2,1].
+In array [2,1,3,1,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5.
+In array [1,7,1,2,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5.
+Both [2,1,3,1,1] and [1,7,1,2,1] have the same dominant element as nums, so this is a valid split.
+It can be shown that index 4 is the minimum index of a valid split.
+```
+
+**Example 3:**
+
+```
+Input: nums = [3,3,3,3,7,2,2]
+Output: -1
+Explanation: It can be shown that there is no valid split.
+```
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-golang-algorithm][me]
+
+[title]: https://leetcode.com/problems/minimum-index-of-a-valid-split
+[me]: https://github.com/kylesliu/awesome-golang-algorithm

leetcode/2701-2800/2780.Minimum-Index-of-a-Valid-Split/Solution.go

@@ -1,5 +1,57 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(nums []int) int {
+	l := len(nums)
+	leftCnt := make(map[int]int)
+	left := make([]int, l)
+	m := -1
+	for i, n := range nums {
+		left[i] = -1
+		leftCnt[n]++
+		if m == -1 {
+			m = n
+			left[i] = m
+			continue
+		}
+		selected := m
+		if leftCnt[n] > leftCnt[m] {
+			selected = n
+		}
+
+		if leftCnt[selected] > (i+1)/2 {
+			left[i] = selected
+		}
+		m = selected
+	}
+
+	rightCnt := make(map[int]int)
+	right := make([]int, l)
+	m = -1
+	for i := l - 1; i >= 0; i-- {
+		n := nums[i]
+		right[i] = -1
+		rightCnt[n]++
+		if m == -1 {
+			m = n
+			right[i] = m
+			continue
+		}
+		selected := m
+		if rightCnt[n] > rightCnt[m] {
+			selected = n
+		}
+		if rightCnt[selected] > (l-i)/2 {
+			right[i] = selected
+		}
+		m = selected
+	}
+	for i := 0; i < l-1; i++ {
+		if left[i] == -1 || right[i] == -1 {
+			continue
+		}
+		if left[i] == right[i+1] {
+			return i
+		}
+	}
+	return -1
 }

leetcode/2701-2800/2780.Minimum-Index-of-a-Valid-Split/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{1, 2, 2, 2}, 2},
+		{"TestCase2", []int{2, 1, 3, 1, 1, 1, 7, 1, 2, 1}, 4},
+		{"TestCase3", []int{3, 3, 3, 3, 7, 2, 2}, -1},
 	}
 
 	//	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() {
 }