[Leetcode] Search in Rotated Sorted Array

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.

画个图比划一下子就清楚了。

class Solution {
public:
    int search(int A[], int n, int target) {
        int l = 0, r = n - 1, m;
        while (l <= r) {
            m = l + (r - l)/2;
            if (A[m] == target) return m;
            if (A[m] < A[r]) {
                if (A[m] <= target && target <= A[r]) l = m + 1;
                else r = m - 1;
            } else {
                if (A[l] <= target && target <= A[m]) r = m - 1;
                else l = m + 1;
            }
        }
        return -1;
    }
};