Leetcode•Sep 11, 2025

Longest Mountain in Array

Hazrat Ali

Leetcode

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


Solution

/**
 * @param {number[]} A
 * @return {number}
 */
const longestMountain = A => {
  let ans = 0;

  for (let i = 0, j = 0, p = -1; j < A.length; j++) {
    if ((j === 0 || A[j] > A[j - 1]) && (j === A.length - 1 || A[j] > A[j + 1])) {
     
      p = j;
    }

    if ((j === 0 || A[j] <= A[j - 1]) && (j === A.length - 1 || A[j] <= A[j + 1])) {
     
      if (p > 0) {
       
        ans = Math.max(ans, j - i + 1);
      }

      i = j;
     
      p = -1;
    }
  }

  return ans;
};





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