https://leetcode.cn/problems/find-peak-element/description/
class Solution {public int findPeakElement(int[] nums) {// 需要依据题意来证明一个定理// i~n-1中切nums[i]<nums[i+1],则i+1~n-1一定存在至少一个峰值// 则峰值具有二段性return lowerBound(nums);}int lowerBound(int[] nums){int l=0,r=nums.length-2;while(l<=r){int mid=l+(r-l>>1);// mid一定不是答案,则答案一定在右侧if(nums[mid]<=nums[mid+1])l=mid+1;else r=mid-1;}return l;}}