Merge pull request #1169 from 0xff-dev/845

Add solution and test-cases for problem 845

Author: 6boris

leetcode/801-900/0845.Longest-Mountain-in-Array/README.md

@@ -1,28 +1,31 @@
 # [845.Longest Mountain in 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 may recall that an array `arr` is a **mountain array** if and only if:
+
+- `arr.length >= 3`
+- There exists some index `i` **(0-indexed)** with `0 < i < arr.length - 1` such that:
+
+    - `arr[0] < arr[1] < ... < arr[i - 1] < arr[i]`
+    - `arr[i] > arr[i + 1] > ... > arr[arr.length - 1]`
+
+Given an integer array `arr`, return the length of the longest subarray, which is a mountain. Return `0` if there is no mountain subarray.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: arr = [2,1,4,7,3,2,5]
+Output: 5
+Explanation: The largest mountain is [1,4,7,3,2] which has length 5.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Longest Mountain in Array
-```go
 ```
-
+Input: arr = [2,2,2]
+Output: 0
+Explanation: There is no mountain.
+```
 
 ## 结语
 

leetcode/801-900/0845.Longest-Mountain-in-Array/Solution.go

@@ -1,5 +1,27 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(arr []int) int {
+	left := make([]int, len(arr))
+	left[0] = 0
+	for i := 1; i < len(arr); i++ {
+		if arr[i] > arr[i-1] {
+			left[i] = left[i-1] + 1
+		}
+	}
+	ans := 0
+	cnt := 0
+	for i := len(arr) - 2; i > 0; i-- {
+		if arr[i] > arr[i+1] {
+			cnt++
+		} else {
+			cnt = 0
+		}
+		if left[i] != 0 && cnt != 0 {
+			ans = max(ans, left[i]+cnt)
+		}
+	}
+	if ans > 0 {
+		ans++
+	}
+	return ans
 }

leetcode/801-900/0845.Longest-Mountain-in-Array/Solution_test.go

@@ -10,12 +10,11 @@ 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, 4, 7, 3, 2, 5}, 5},
+		{"TestCase2", []int{2, 2, 2}, 0},
 	}
 
 	//	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() {
 }