Longest Mountain in Array

Description

Let's call any (contiguous) subarray B (of A) a mountain if the following properties hold:

• B.length >= 3
• There exists some 0 < i < B.length - 1 such that B[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1]

(Note that B could be any subarray of A, including the entire array A.)

Given an array A of integers, return the length of the longest mountain. 

Return 0 if there is no mountain.

Example 1:

Input: [2,1,4,7,3,2,5]
Output: 5
Explanation: The largest mountain is [1,4,7,3,2] which has length 5.

Example 2:

Input: [2,2,2]
Output: 0
Explanation: There is no mountain.

Note:

1. 0 <= A.length <= 10000
2. 0 <= A[i] <= 10000

Follow up:

• Can you solve it using only one pass?
• Can you solve it in O(1) space?

Solution(javascript)

/*
 * @lc app=leetcode id=845 lang=javascript
 *
 * [845] Longest Mountain in Array
 */

// @lc code=start
/**
 * @param {number[]} A
 * @return {number}
 */
const longestMountain = function (A) {
  let max = 0
  for (let left = 0; left < A.length; left++) {
    let right = left
    while (A[right] < A[right + 1]) {
      right++
    }
    const top = right
    while (right > left && A[right] > A[right + 1]) {
      right++
    }
    if (right > top && top > left) {
      max = Math.max(max, right - left + 1)
      left = right
      left--
    }
  }
  return max
}
// @lc code=end