Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). You are given a target value to search. If found in the array return its index, otherwise return -1. You may assume no duplicate exists in the array. http://leetcode.com/onlinejudge#question_33

leetcode_search_in_rotated_sorted_array.cpp

class Solution {
public:
    int search(int A[], int n, int target) {
        int ans = -1;
        int left = 0, right = n - 1;
        while (left <= right) {
            int mid = (left + right) >> 1;
            if (A[mid] == target) {
                ans = mid;
                break;
            }
            if (A[mid] >= A[0]) {
                if (target > A[mid])
                    left = mid + 1;
                else if (target < A[0])
                    left = mid + 1;
                else
                    right = mid - 1;
            }
            else {
                if (target < A[mid])
                    right = mid - 1;
                else if (target <= A[n - 1])
                    left = mid + 1;
                else
                    right = mid - 1;
            }
        }
        return ans;
    }
};