LeetCode Online Judge 题目C# 练习 - 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.

 1         public static int SearchinRotatedSortedArray(int[] A, int target)

 2         {

 3             return BinarySearchRotatedSortedArray(A, 0, A.Length - 1, target);

 4         }

 5 

 6         public static int BinarySearchRotatedSortedArray(int[] A, int l, int r, int target)

 7         {

 8             if (l > r)

 9                 return -1;

10 

11             int m = (l + r) / 2;

12 

13             if (target == A[m])

14                 return m;

15 

16             if (A[m] >= A[l])

17             {

18                 if (target >= A[l] && target < A[m])

19                     r = m - 1;

20                 else

21                     l = m + 1;

22 

23                 return BinarySearchRotatedSortedArray(A, l, r, target);

24             }

25             else

26             {

27                 if (target > A[m] && target <= A[r])

28                     l = m + 1;

29                 else

30                     r = m - 1;

31 

32                 return BinarySearchRotatedSortedArray(A, l, r, target);

33             }

34         }

代码分析：

　　同样是binary search 的变形。每次往下找，到底是找 前半部 还是 后半部， 要根据情况两种情况。

　　1. A[m] >= A[l], 前半部分是sorted的。

　　2. A[m] < A[l]， 后半部分是sorted的。