845. Longest Mountain in Array LeetCode Solution

In this guide, you will get 845. Longest Mountain in Array LeetCode Solution with the best time and space complexity. The solution to Longest Mountain in Array problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Problem Statement
Complexity Analysis
Longest Mountain in Array solution in C++
Longest Mountain in Array solution in Java
Longest Mountain in Array solution in Python
Additional Resources

845. Longest Mountain in Array LeetCode Solution image

Problem Statement of Longest Mountain in Array

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 + 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?

Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(1)

845. Longest Mountain in Array LeetCode Solution in C++

class Solution {
 public:
  int longestMountain(vector<int>& arr) {
    int ans = 0;

    for (int i = 0; i + 1 < arr.size();) {
      while (i + 1 < arr.size() && arr[i] == arr[i + 1])
        ++i;

      int increasing = 0;
      int decreasing = 0;

      while (i + 1 < arr.size() && arr[i] < arr[i + 1]) {
        ++increasing;
        ++i;
      }

      while (i + 1 < arr.size() && arr[i] > arr[i + 1]) {
        ++decreasing;
        ++i;
      }

      if (increasing > 0 && decreasing > 0)
        ans = max(ans, increasing + decreasing + 1);
    }

    return ans;
  }
};
/* code provided by PROGIEZ */

845. Longest Mountain in Array LeetCode Solution in Java

class Solution {
  public int longestMountain(int[] arr) {
    int ans = 0;

    for (int i = 0; i + 1 < arr.length;) {
      while (i + 1 < arr.length && arr[i] == arr[i + 1])
        ++i;

      int increasing = 0;
      int decreasing = 0;

      while (i + 1 < arr.length && arr[i] < arr[i + 1]) {
        ++increasing;
        ++i;
      }

      while (i + 1 < arr.length && arr[i] > arr[i + 1]) {
        ++decreasing;
        ++i;
      }

      if (increasing > 0 && decreasing > 0)
        ans = Math.max(ans, increasing + decreasing + 1);
    }

    return ans;
  }
}
// code provided by PROGIEZ

845. Longest Mountain in Array LeetCode Solution in Python

class Solution:
  def longestMountain(self, arr: list[int]) -> int:
    ans = 0
    i = 0

    while i + 1 < len(arr):
      while i + 1 < len(arr) and arr[i] == arr[i + 1]:
        i += 1

      increasing = 0
      decreasing = 0

      while i + 1 < len(arr) and arr[i] < arr[i + 1]:
        increasing += 1
        i += 1

      while i + 1 < len(arr) and arr[i] > arr[i + 1]:
        decreasing += 1
        i += 1

      if increasing > 0 and decreasing > 0:
        ans = max(ans, increasing + decreasing + 1)

    return ans
 # code by PROGIEZ