852. 山脉数组的峰顶索引

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class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        // 二分查找
        int i = 0;
        int j = arr.length - 1;

        while(true){
            int mid = (i + j)/2;
            if(arr[mid] > arr[mid-1] && arr[mid] > arr[mid+1]){
                return mid;
            }else if(arr[mid]>arr[mid-1]){
                i = mid;
            }else if(arr[mid]<arr[mid-1]){
                j = mid;
            }
        }
    }
}