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

int get_biggest(int A[], int n) {
    int ret = 0;
    int left = 0;
    int right = n - 1;
    while (left <= right) {
        int mid = (left + right) >> 1;
        if (A[mid] >= A[0]) {
            ret = max(ret, mid);
            left = mid + 1;
        }
        else
            right = mid - 1;
    }
    return ret;
}

int bsearch(int A[], int left, int right, int target) {
    while (left <= right) {
        int mid = (left + right) >> 1;
        if (A[mid] > target)
            right = mid - 1;
        else if (A[mid] < target)
            left = mid + 1;
        else
            return mid;
    }
    return -1;
}

class Solution {
public:
    int search(int A[], int n, int target) {
        if (n == 0)
            return -1;
        if (A[0] < A[n - 1])
            return bsearch(A, 0, n - 1, target);
        else {
            int bigid = get_biggest(A, n);
            if (target >= A[0])
                return bsearch(A, 0, bigid, target);
            else
                return bsearch(A, bigid + 1, n - 1, target);
        }
    }
};