HackerHeap

Suppose an array sorted in ascending order 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.

Your algorithm’s runtime complexity must be in the order of O(log n).

Example 1:

Input: nums = [4,5,6,7,0,1,2], target = 0
Output: 4

Example 2:

Input: nums = [4,5,6,7,0,1,2], target = 3
Output: -1

Solution 1:

public class Solution {
    public int search(int[] nums, int target) {
        return binarySearch(nums,target,0,nums.length-1);
    }
    
    public int binarySearch(int[] nums, int target, int start, int end){
        if(start>end)return -1;
        int mid = start+(end-start)/2;
        if(nums[mid] == target) return mid;
        if(nums[start]<=nums[mid]){
            if(nums[start]<=target && target<nums[mid]){
                return binarySearch(nums,target,start,mid-1);
            }else{
                return binarySearch(nums,target,mid+1,end);
            }
        }else{
            if(nums[mid]<target && target<=nums[end]){
                return binarySearch(nums,target,mid+1,end);
            }else{
                return binarySearch(nums,target,start,mid-1);
            }
        }
    }
}