LeetCode：(Array-33)Search in Rotated Sorted Array

去哪网面试题:二分查找的变形题目

　　目的是为了在O(logn)的时间复杂度下解决此问题，所以用二分查找。

 

 1 package com.hb.leetcode;

 2 

 3 

 4 /*

 5  * Search in Rotated Sorted  Array

 6  * 

 7  * Suppose a sorted array is rotated at some pivot unknown to you beforehand.

 8  * (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

 9  * You are given a target value to search. 

10  * If found in the array return its index, otherwise return -1.

11  * You may assume no duplicate exists in the array.

12  * 

13  */

14 

15 public class SearchInRotated {

16     

17     public  static int search(int[] A , int  target){

18         return rec( A , target , 0 , A.length -1 );

19     }

20      

21     public  static int rec(int[]  A , int target , int  low , int  high){

22         if(low > high){  //没找到的情况

23             return -1 ;  

24         } 

25         

26         int  mid = low + (high - low) / 2 ;

27         

28         if(A[mid] == target){  //找到了

29             return mid;

30         }

31         

32         int res = rec(A , target , low , mid -1 );  //在左侧查找 

33         

34         if(res == -1 ){  //如果左侧没有找到，继续在右侧查找

35             res = rec(A , target , mid + 1 , high ); 

36         }

37         

38         

39         return res;

40     }

41     

42     public static void main(String[] args) {

43         int[]  A = { 2, 3, 4, 5, 6, 0 ,1};

44         System.out.println(search(A, 0));

45     }

46     

47     

48 

49 }