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.

题目解析：

（1）要找峰值，如果当前那个点是下降的，那肯定是在前面

（2）如果当前那个点是上升的，那肯定是在后面。

跟跑山道理是相同的啊

#include <iostream>#include <vector>using namespace std;int findPeakElement(const vector<int> &num) {int size = num.size();if(size <= 1 )return 0;int begin = 0;int end = size - 1;int mid = (begin+end)/2;while(begin <= end){int midBer = mid - 1;int midAft = mid + 1;if(midBer < 0 && num[mid] > num[midAft])return mid;if(midAft >= size && num[mid] > num[midBer] )return mid;if(num[mid] > num[midBer] && num[mid] > num[midAft])return mid;if(num[mid] < num[midBer] && num[mid] > num[midAft])end = mid-1;else if(num[mid] > num[midBer] && num[mid] < num[midAft])begin = mid + 1;else if(num[mid] < num[midBer] && num[mid] < num[midAft])begin = mid + 1;mid = (begin+end)/2;}return 0;}int main(void){vector<int> num;num.push_back(6);num.push_back(5);num.push_back(4);num.push_back(3);cout << findPeakElement(num) << endl;system("pause");return 0;}