题目:
There is an integer array which has the following features:
- The numbers in adjacent positions are different.
- A[0] < A[1] && A[A.length - 2] > A[A.length - 1].
We define a position P is a peek if:
A[P] > A[P-1] && A[P] > A[P+1]
Find a peak element in this array. Return the index of the peak.
Example
Given [1, 2, 1, 3, 4, 5, 7, 6]
Return index 1
(which is number 2) or 6
(which is number 7)
题解:
class Solution { public: /** * @param A: An integers array. * @return: return any of peek positions. */ int findPeak(vector<int> A) { if (A.size() < 3) { return -1; } int n = A.size(); int start = 1; int end = n - 1; while (start < end - 1) { int mid = start + (end - start) / 2; if (A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) { return mid; } else if (A[mid] > A[mid-1]) { start = mid; } else { end = mid; } } if (A[start] > A[start + 1]) { return start; } else if (A[end] > A[end - 1]) { return end; } return -1; } };