Search in Rotated Sorted Array


#1

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

#2

The below solution uses modified binary search forcing the lower or upper boundary based on the where the target could be. Below is the Go solution.

func search(nums []int, target int) int {
    l, r := 0, len(nums)-1
    for l<=r{
        m := (l+r)/2
        if nums[m] == target {
            return m
        }else if nums[l]<=nums[m]{
            if target >= nums[l] && target < nums[m]{
                r = m-1
            } else {
                l = m+1
            }
        } else {
            if target>nums[m] && target<=nums[r]{
                l = m+1
            } else {
                r = m-1
            }
        }
    }
    
    return -1
}