Valid Mountain Array Problem
Description
LeetCode Problem 941.
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:
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Input: arr = [2,1]
Output: false
Example 2:
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Input: arr = [3,5,5]
Output: false
Example 3:
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Input: arr = [0,3,2,1]
Output: true
Constraints:
- 1 <= arr.length <= 10^4
- 0 <= arr[i] <= 10^4
Sample C++ Code
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class Solution {
public:
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;
}
};