LeetCode-in-Java

845. Longest Mountain in Array

Medium

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.

Constraints:

• 1 <= arr.length <= 104
• 0 <= arr[i] <= 104

Follow up:

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

Solution

public class Solution {
    public int longestMountain(int[] arr) {
        int s = 0;
        int i = 1;
        while (i < arr.length - 1) {
            if (arr[i] > arr[i - 1] && arr[i] > arr[i + 1]) {
                int j = i;
                int tem = 1;
                while (j > 0 && arr[j] > arr[j - 1]) {
                    j--;
                    tem++;
                }
                j = i;
                while (j < arr.length - 1 && arr[j] > arr[j + 1]) {
                    j++;
                    tem++;
                }
                s = Math.max(s, tem);
                i = j;
            }
            i++;
        }
        return s;
    }
}

This site is open source. Improve this page.