[LeetCode]Find Peak Element

寻找峰值元素的二分搜索算法

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本文介绍了一个使用二分搜索法解决寻找峰值元素问题的算法，详细解释了如何在给定数组中找到大于其相邻元素的元素，并提供了代码实现。

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.

LeetCode Source\

Analysis：

This problem is a binary search,but we should do a litte change.

the PeakElement is the largest in the neighbor,when our elment is small than the next one it means that the peak is in the [mid+1,left],else the peak is in the [right,mid].

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