Rotate Array

Solution

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

 

Example

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]

 

class Solution {
    public void rotate(int[] nums, int k) {
        k %= nums.length;
        reverse(nums, 0, nums.length -1);
        reverse(nums, 0, k-1);
        reverse(nums, k, nums.length -1);
    }
    
    private void reverse(int[] nums, int s, int e){
        while(s < e){
            int tmp = nums[s];
            nums[s] = nums[e];
            nums[e] = tmp;
            s++;
            e--;
        }
    }
}

 

Explanation:

1. First, calculate k %= nums.length to handle cases where k is greater than the array's length.
2. Reverse the entire array.
3. Reverse the first k elements (which will move them into their final positions at the end).
4. Reverse the remaining elements from k to the end of the array, placing them in their correct positions at the start.

In the reverse method, the array (or part of it) is reversed by repeatedly swapping elements at the start (s) and end (e) indices, and moving inward until s is no longer less than e.