leetcode 之Search in Rotated Sorted Array（三）

描述
    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.

二分法查找适用于排好序的，所以这题的关键是如何确定某部分的顺序是怎样的。

 1 int searchRotateSA(int A[], int n,int target)
 2 {
 3     int first = 0, last = n;
 4     while (first!=last)
 5     {
 6         int mid = first + (last - first) / 2;
 7         if (A[mid] = target)
 8         {
 9             return mid;
10         }
11         else if (A[first]<=A[mid])//判断大小顺序
12         {
13             if (A[first] <= target&&target <= A[mid])
14                 last = mid;
15             else
16                 first = mid + 1;
17         }
18         else
19         {
20             if (A[first] >= target&& A[mid] <= target)
21                 last = mid;
22             else
23                 first = mid + 1;
24
25         }
26     }
27
28     return -1;
29 }