[LintCode] 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.

Example

For [4, 5, 1, 2, 3] and target=1, return 2.

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

Challenge 

O(logN) time

 

A rotated sorted array has a split point where one side of this point is sorted, the other side is not.

public class Solution {
    /** 
     *@param A : an integer rotated sorted array
     *@param target :  an integer to be searched
     *return : an integer
     */
    public int search(int[] A, int target) {
        if(A == null || A.length == 0)
        {
            return -1;
        }
        return searchHelper(A, target, 0, A.length - 1);
    }
    
    private int searchHelper(int[] A, int target, int startIdx, int endIdx)
    {
        if(startIdx > endIdx)
        {
            return -1;
        }
        
        int mid = startIdx + (endIdx - startIdx) / 2;
        
        if(A[mid] == target)
        {
            return mid;
        }
        //right half sorted
        else if(A[mid] < A[endIdx])
        {
            //if target in range of right half
            if(target > A[mid] && target <= A[endIdx])
            {
                return searchHelper(A, target, mid + 1, endIdx);
            }
            //search left half otherwise 
            else
            {
                return searchHelper(A, target, startIdx, mid - 1);
            }
        }
        //left half sorted 
        else
        {
            //if target in range of left half
            if(target >= A[startIdx] && target < A[mid])
            {
                return searchHelper(A, target, startIdx, mid - 1);
            }
            //search right half otherwise
            else
            {
                return searchHelper(A, target, mid + 1, endIdx);
            }
        }
    }
}

 

 

Related Problems

Search in Rotated Sorted Array II

Search a 2D Matrix