Leetcode#33

Search in Rotated Sorted Array

Problem Statement

There is an integer array nums sorted in ascending order (with distinct values).

Prior to being passed to your function, nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k], nums[k+1], ..., nums[n-1], nums[0], nums[1], ..., nums[k-1]] (0-indexed). For example, [0,1,2,4,5,6,7] might be rotated at pivot index 3 and become [4,5,6,7,0,1,2].

Given the array nums after the possible rotation and an integer target, return the index of target if it is in nums, or -1 if it is not in nums.

You must write an algorithm with O(log n) runtime complexity.

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

Example 3:

Input: nums = [1], target = 0
Output: -1

Constraints:

• 1 <= nums.length <= 5000
• -104 <= nums[i] <= 104
• All values of nums are unique.
• nums is an ascending array that is possibly rotated.
• -104 <= target <= 104

Logic

Please read normal Binary search code for finding target and its comparison with rotated array.

This will help to build foundation.

• Binary Search vs Rotated Binary Search

Golang Solution

func search(nums []int, target int) int {

	left, right := 0, len(nums)-1

	for left <= right {
		middle := left + (right-left)/2

		// check for target comparison
		if nums[middle] == target {
			return middle
		}

		// left half is sorted
		// compare left and middle
		if nums[left] <= nums[middle] {
			// compare left, target & middle
			if nums[left] <= target && target < nums[middle] {
				right = middle - 1
			} else {
				left = middle + 1
			}
		} else {
			// right half is sorted
			if nums[middle] < target && target <= nums[right] {
				left = middle + 1
			} else {
				right = middle - 1
			}
		}
	}

	return -1
}

Output

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

Output
4

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