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.

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Note:

Your solution should be in logarithmic complexity.

解题技巧：

该题是在一个相邻元素不相等的数组，找出其中的一个局部最大值，返回其对应下标,要求时间复杂度为O(lgN)。因此，可以采用二分查找法，即：如

果中间元素大于其相邻后续元素，则中间元素左侧(包含该中间元素）必包含一个局部最大值。如果中间元素小于其相邻后续元素，则中间元素右侧必

包含一个局部最大值。

代码：

#include <iostream>#include <vector>using namespace std;int findPeakElement(const vector<int> &num){    int left=0,right=num.size()-1;    while(left <= right)    {        if(left == right) return left;        int mid = (left + right) / 2;        if(num[mid] < num[mid+1])            left = mid+1;        else            right = mid;    }}int main(){    vector<int> num;    int x;    while(cin >> x)    {        num.push_back(x);    }    cout<<findPeakElement(num);}