941. Valid Mountain Array

Problem Statement

Easy

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

C++

Source file

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