0852-peak-index-in-a-mountain-array.java

class Solution {

    public int peakIndexInMountainArray(int[] arr) {
        int left = 0, right = arr.length - 1;
        int res = -1;

        while (left <= right) {
            int mid = left + (right - left + 1) / 2;

            if (arr[mid - 1] <= arr[mid]) {
                left = mid + 1;
                res = mid;
            } else {
                right = mid - 1;
            }
        }

        return res;
    }
}