162 Find Peak Element

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.

要求算法：logn复杂度

 

因为num[i] ≠ num[i+1]，可以想象数组是一个几个驼峰链接成的曲线，利用二分搜索找驼峰的顶点。

 

int findPeakElement(vector<int>& nums) {
        if(nums.size()==0)return 0;
        int left = 0;
        int right = nums.size()-1;
        while(left<right){
            int mid = (left+right)/2;
            if(nums[mid]<nums[mid+1])
                left = mid+1;
            else
                right = mid;
        }
        return left;
    }