[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。

 1 class Solution {

 2 public:

 3     int search(int A[], int n, int target) {

 4         int l = 0, r = n - 1, m;

 5         while (l <= r) {

 6             m = l + (r - l)/2;

 7             if (A[m] == target) return m;

 8             if (A[m] < A[r]) {

 9                 if (A[m] <= target && target <= A[r]) l = m + 1;

10                 else r = m - 1;

11             } else {

12                 if (A[l] <= target && target <= A[m]) r = m - 1;

13                 else l = m + 1;

14             }

15         }

16         return -1;

17     }

18 };