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# Valid Mountain Array LeetCode Solution

## Problem – Valid Mountain Array LeetCode Solution

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 < arr < ... < 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`

### Valid Mountain Array LeetCode Solution in C++

``````    bool validMountainArray(vector<int>& A) {
int n = A.size(), i = 0, j = n - 1;
while (i + 1 < n && A[i] < A[i + 1]) i++;
while (j > 0 && A[j - 1] > A[j]) j--;
return i > 0 && i == j && j < n - 1;
}
``````

### Valid Mountain Array LeetCode Solution in Java

``````    public boolean validMountainArray(int[] A) {
int n = A.length, i = 0, j = n - 1;
while (i + 1 < n && A[i] < A[i + 1]) i++;
while (j > 0 && A[j - 1] > A[j]) j--;
return i > 0 && i == j && j < n - 1;
}
``````

### Valid Mountain Array LeetCode Solution in Python

``````    def validMountainArray(self, A):
i, j, n = 0, len(A) - 1, len(A)
while i + 1 < n and A[i] < A[i + 1]: i += 1
while j > 0 and A[j - 1] > A[j]: j -= 1
return 0 < i == j < n - 1
``````
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