941. Valid Mountain Array.cpp

//link: https://leetcode.com/problems/valid-mountain-array/

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

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

A.length >= 3
There exists some i with 0 < i < A.length - 1 such that:
A[0] < A[1] < ... A[i-1] < A[i]
A[i] > A[i+1] > ... > A[A.length - 1]

Example 1:

Input: [2,1]
Output: false
Example 2:

Input: [3,5,5]
Output: false
Example 3:

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

Note:

0 <= A.length <= 10000
0 <= A[i] <= 10000 
*/

/*
Result:
Runtime: 68 ms, faster than 21.72% of C++ online submissions for Valid Mountain Array.
Memory Usage: 22.6 MB, less than 6.25% of C++ online submissions for Valid Mountain Array.
*/

class Solution {
public:
    bool validMountainArray(vector<int>& A) {
        if(A.size() <= 2){
            return false;
        }
        int i = 0;
        while(i < A.size() - 1 && A[i + 1] > A[i]){
            i ++;
        }
        if(i == A.size() - 1 || i == 0){
            return false;
        }
        
        while(i < A.size() - 1 && A[i + 1] < A[i]){
            i ++;
        }
        
        return i == A.size() - 1;
    }
};