Peak_Index_in_a_Mountain_Array.java

//Leetcode 852. Peak Index in a Mountain Array
//Question - https://leetcode.com/problems/peak-index-in-a-mountain-array/

/*Let's call an array A a mountain if the following properties hold:

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

Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].

Example 1:

Input: [0,1,0]
Output: 1

Example 2:

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

Note:

    3 <= A.length <= 10000
    0 <= A[i] <= 10^6
    A is a mountain, as defined above.

*/

class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int low = 0;
        int high = A.length-1;
        int ans = -1;
        
        while(low <= high){
            int mid = low + (high-low)/2;
            if(A[mid] < A[mid+1]) low = mid + 1;
            else{
                ans = mid;
                high = mid-1;
            }
        }
        return ans;
    }

}

//OR

class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int low = 0;
        int high = A.length-1;
        
        while(low < high){
            int mid = low + (high-low)/2;
            if(A[mid] < A[mid+1]) low = mid + 1;
            else{
                high = mid;
            }
        }
        return low;
    }

}