162. Find Peak Element

1. class Solution {  
2. public:  
3.     int findPeakElement(const vector<int> &num) {  
4.          return findPeakElement(num,0,num.size()-1);  
5.     }  
6. private:  
7.     int findPeakElement(const vector<int> &num,int start,int end){  
8.          if (start==end) return start;  
9.          if(end-start==1) return num[start]>num[end]?start:end;  
10.          int mid=(end+start)/2;  
11.          if(num[mid]>num[mid-1]&&num[mid]>num[mid+1]) return mid;  
12.          else if(num[mid]<num[mid-1])  return findPeakElement(num,start,mid-1);  
13.          else return findPeakElement(num,mid+1,end);  
14.     }  
15. };