Algorithm

Problem Name: 941. Valid Mountain Array

Problem Link: https://leetcode.com/problems/valid-mountain-array/
 

Given an array of integers arr, return true if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:

  • arr.length >= 3
  • There exists some i 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]

 

Example 1:

Input: arr = [2,1]
Output: false

Example 2:

Input: arr = [3,5,5]
Output: false

Example 3:

Input: arr = [0,3,2,1]
Output: true

 

Constraints:

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

Code Examples

#1 Code Example with C++ Programming

Code - C++ Programming


class Solution {
public:
    bool validMountainArray(vector<int>& A) {
        int i = 0, n = A.size();
        if (n  <  3) {
            return false;
        }
        while (i < n - 1 && A[i] < A[i + 1]) {
            ++i;
        }
        if (i == 0 || i == n - 1) {
            return false;
        }
        while (i  <  n - 1 && A[i] > A[i + 1]) {
            ++i;
        }
        return i == n - 1;
    }
};
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Input

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arr = [2,1]

Output

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false

#2 Code Example with Java Programming

Code - Java Programming


class Solution {
  public boolean validMountainArray(int[] A) {
    if (A.length < 3) {
      return false;
    }
    int idx = 0;
    int n = A.length;
    while (idx + 1  <  n && A[idx] < A[idx + 1]) {
      idx++;
    }
    if (idx == 0 || idx == n - 1) {
      return false;
    }
    while (idx + 1  <  n && A[idx] > A[idx + 1]) {
      idx++;
    }
    return idx == n - 1;
  }
}
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Input

x
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arr = [2,1]

Output

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false

#3 Code Example with Javascript Programming

Code - Javascript Programming


const validMountainArray = function(A) {
  if (A.length < 3) return false;
  let start = 0;
  let end = A.length - 1;
  while (start  <  end) {
    while (A[end - 1] > A[end]) {
      end--;
    }
    while (A[start] < A[start + 1]) {
      start++;
    }
    if (start !== end || start === 0 || end === A.length - 1) return false;
  }
  return true;
};
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Input

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arr = [3,5,5]

Output

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false

#4 Code Example with Python Programming

Code - Python Programming


class Solution:
    def validMountainArray(self, A):
        i = A and A.index(max(A))
        return A and 0a3 for a2,a3 in zip(A[i:],A[i+1:])) or False
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Input

x
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arr = [3,5,5]

Output

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false

#5 Code Example with C# Programming

Code - C# Programming


namespace LeetCode
{
    public class _0941_ValidMountainArray
    {
        public bool ValidMountainArray(int[] A)
        {
            int i = 0, N = A.Length;

            while (i + 1  <  N && A[i] < A[i + 1])
                i++;

            if (i == 0 || i == N - 1) return false;

            while (i + 1  <  N && A[i] > A[i + 1])
                i++;

            return i == N - 1;
        }
    }
}
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Input

x
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arr = [0,3,2,1]

Output

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true
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