class Solution {    
    public static int peakIndexInMountainArray(int[] arr) {
        int start = 0;
        int end = arr.length-1;

        while(start < end){
            int mid = start + (end-start)/2;

            if (arr[mid] > arr[mid+1]) end = mid;
            else start = mid+1;
        }
        return start;
    }
}