Solving LeetCode Problem 189: Rotate Array (Part 1)

Welcome to the first part of our series on solving Leetcode Problem 189, Rotate Array. In this video, we’ll tackle the problem using a brute force approach with a time complexity of O(n^2).

Problem Description

Given an integer array nums, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

Input: nums = [-1,-100,3,99], k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

Constraints:

1 <= nums.length <= 105
-231 <= nums[i] <= 231 - 1
0 <= k <= 105

Solution

class Solution {
    public void rotate(int[] nums, int k) {
        for(int i = 0; i < k; i++) {
           rotateOneItem(nums); 
        }
    }

    private void rotateOneItem(int[] nums) {
        int last = nums[nums.length - 1];
        for(int i = nums.length - 2; i >= 0; i--) {
            nums[i + 1] = nums[i];
        }
        nums[0] = last;
    }
}

In this YouTube video, I was explained how to solve this problem step by step.