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:


 

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:

  1. 0 <= A.length <= 10000
  2. 0 <= A[i] <= 10000 

Solution:

class Solution {
    public boolean validMountainArray(int[] A) {
        if (A.length < 3) return false;
        boolean up = false;
        boolean down = false;
        int prev = A[0];
        for (int i = 1; i < A.length; i ++) {
            int curr = A[i];
            if (curr == prev) return false;
            if (curr > prev) {
                up = true;
                if (down) return false;
            } else {
                down = true;
                if (!up) return false;
            }
            prev = curr;
        }
        return up && down;
    }
}