```
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;
}
};
```

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].