62.Search in Rotated Sorted Array

1.Description(Medium)

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

(i.e.,0 1 2 4 5 6 7might become4 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.

Example

For[4, 5, 1, 2, 3]andtarget=1, return2.

For[4, 5, 1, 2, 3]andtarget=0, return-1.

Challenge

O(logN) time

Tags

Binary Search LinkedIn Array Facebook Sorted Array Uber

2.Code

注意分两种情况，看mid在pivot的哪边。

public int search(int[] A, int target) {
        if(A==null || A.length==0){
            return -1;
        }
        int left=0;
        int right=A.length-1;
        while(left+1<right){
            int mid=left+(right-left)/2;
            if(A[mid]==target){
                return mid;
            }
            //situation 1:
            if(A[left]>A[mid]){
                if(A[mid]<target && target<=A[right]){
                    left=mid;
                }
                else{
                    right=mid;
                }
            }
            //situation 2:
            if(A[left]<=A[mid]){
                if(A[left]<=target && target<A[mid]){
                    right=mid;
                }
                else{
                    left=mid;
                }
            }
        }
        if(A[left]==target){
            return left;
        }
        if(A[right]==target){
            return right;
        }
        return -1;
    }