Rotate Array Java Solution - The Coding Shala

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Rotate Array

Problem:

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

Example 1:
Input: [1,2,3,4,5,6,7] and 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: [-1,-100,3,99] and 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]

Rotate Array Java Solution

Approach 1: 
We can use an extra array. Time complexity will be O(n) and Space Complexity will be O(n).

Java 

class Solution {
    public void rotate(int[] nums, int k) {
        int len = nums.length;
        k = k%len;
        int[] tmp = new int[len];
        for(int i = 0; i<len; i++) tmp[i] = nums[(i+len-k)%len];
        for(int i=0;i<len;i++) nums[i] = tmp[i];
    }
}

Approach 2:
Using the reverse of an array.
Time Complexity O(n).
Space Complexity O(1).

Java 

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



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