[leetcode]Find Peak Element

类似二分。

class Solution {

public:

    int findPeakElement(const vector<int> &num) {

        int size = num.size();

        int left = 0;

        int right = size - 1;

        while (left <= right) {

            int mid = (left + right) / 2;

            if ((mid == 0 || num[mid] > num[mid-1]) &&

                (mid == size - 1 || num[mid] > num[mid+1])) {

                return mid;

            }

            if (mid != 0 && num[mid] < num[mid-1]) {

                right = mid - 1;

            } else {

                left = mid + 1;

            }

        }

        return -1;

    }

};