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.

统计数学规律，二分法实现

1. int target;
2. bool findPeakElement(const vector<int> &num,int start,int end) {
3. if(end == start) {
4. target = start;
5. return true;
6. }
7. int mid = start + (end - start)/2;
8. if(num[mid] < num[mid+1]) {
9. start = mid+1;
10. } else {
11. end = mid;
12. }
13. if(findPeakElement(num,start,end)) {
14. return true;
15. }
16. return false;
17. }
18. int findPeakElement(const vector<int> &num) {
19. int nSize = num.size();
20. if(nSize == 0) return -1;
21. target = -1;
22. findPeakElement(num,0,nSize-1);
23. return target;
24. }