arrayMountain.java

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


class Solution {
    public boolean validMountainArray(int[] A) {
        
        int len = A.length -1;
        
        int i = 0;
        
        while(i < len){
            if(A[i] < A[i+1]){
                i++;
            } else {
                break;
            }
        }
        
        if(i == 0 || i == len){
            return false;
        }
        
        while(i < len){
            if(A[i] > A[i+1]){
                i++;
            } else {
                break;
            }
        }
    return i == len;}
}