// 1. 二段性-> 极值点必定存在且单调
class Solution {
    public int findPeakElement(int[] nums) {
        int l = 0 , r = nums.length-1;
        while (l < r){
            int mid = (l + r) >> 1;
            if (nums[mid] > nums[mid +1 ]) r  = mid;
            else l = mid + 1 ;
        }
        return l;
    }
}