leetcode题解：Search in Rotated Sorted Array（旋转排序数组查找）

题目：

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.

说明：

1）已排序数组查找采用二分查找

2）关键找到临界点

实现：

一、我的代码：

 1 class Solution {
 2 public:
 3     int search(int A[], int n, int target) {
 4         if(n==0||n==1&&A[0]!=target) return -1;
 5         if(A[0]==target) return 0;
 6         int i=1;
 7         while(A[i-1]<A[i])  i++;
 8
 9         int pre=binary_search(A,0,i,target);
10         int pos=binary_search(A,i,n-i,target);
11         return pre==-1?pos:pre;
12     }
13 private:
14     int binary_search(int *B,int lo,int len,int goal)
15     {
16         int low=lo;
17         int high=lo+len-1;
18         while(low<=high)
19         {
20             int middle=(low+high)/2;
21             if(goal==B[middle])//找到，返回index
22                return middle;
23             else if(B[middle]<goal)//在右边
24                low=middle+1;
25             else//在左边
26                high=middle-1;
27         }
28         return -1;//没有，返回-1
29     }
30 };

二、网上开源代码：

 1 class Solution {
 2 public:
 3     int search(int A[], int n, int target) {
 4         int first = 0, last = n-1;
 5         while (first <= last)
 6         {
 7             const int mid = (first + last) / 2;
 8             if (A[mid] == target)
 9                 return mid;
10             if (A[first] <= A[mid])
11             {
12                 if (A[first] <= target && target < A[mid])
13                    last = mid-1;
14                 else
15                    first = mid + 1;
16             }
17             else
18             {
19                 if (A[mid] < target && target <= A[last])
20                     first = mid + 1;
21                 else
22                     last = mid-1;
23             }
24         }
25         return -1;
26     }
27 };

leetcode题解：Search in Rotated Sorted Array（旋转排序数组查找）,布布扣,bubuko.com