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
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;
}
}