search_rotated_array.cpp

/*
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.
*/

class Solution {
public:
    int search(int A[], int n, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int lo = 0;
        int hi = n - 1;

        while (lo <= hi) {
            int mid = lo + (hi - lo) / 2;
            if (A[mid] == target) return mid;

            if (A[lo] <= A[mid]) { // first part is sorted
                if (A[mid] > target && target >= A[lo])
                    hi = mid - 1;
                else
                    lo = mid + 1;
            } else { // latter part is sorted
                if (A[mid] < target && target <= A[hi])
                    lo = mid + 1;
                else
                    hi = mid - 1;
            }
        }

        return -1;
    }
};