lc852. 山脉数组的峰顶索引

题目链接：852. 山脉数组的峰顶索引 - 力扣（LeetCode） (leetcode-cn.com)

题解

三分搜索

参考代码

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& a) {
        int l = 0;
        int r = a.size()-1;
        while(l<r) {
            int m = l + (r-l) /2;
            int ml = l + (m-l)/2 ;
            int mr = r - (r-m) / 2;
            // cout<<m<<" "<<l<<" "<<r<<" "<<ml<<" "<<mr<<endl;
            if(a[ml]>=a[mr]) {
                r = mr-1;
            } else if(a[ml]<a[mr]) {
                l = ml+1;
            }
        }
        return l;
    }
};