We use cookies to ensure you have the best browsing experience on our website. Please read our cookie policy for more information about how we use cookies.
  1. Practice
  2. Tutorials
  3. Cracking the Coding Interview
  4. Arrays: Left Rotation
  5. Discussions

Arrays: Left Rotation

  • darkOverLord + 6 comments

    I did it this way, in Java

    public static int[] arrayLeftRotation(int[] a, int n, int k) {
        if (k >= n) {
            k = k % n;
        }
        
        if (k == 0) return a;
        
        int[] temp = new int[n];
        
        for (int i = 0; i < n; i++) {
            if (i + k < n) {
                temp[i] = a[i + k];
            } else {
                temp[i] = a[(i + k) - n];
            }
        }
        
        return temp;
    }
    • vinaysh + 1 comment

      instead of if-else statement temp[i] = a[(i+k)%n]; would be enough.

      Also this solution would take up extra memory(for temp).

      • shortcut2alireza + 2 comments

        Would you mind sharing your solution that does it in-place? Thanks

        • jacob0306 + 1 comment

          in case you need it! hope it help!

          import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();
        int a[] = new int[n];
        
        for(int a_i=0; a_i < n; a_i++){
            a[((n- (k%n))+a_i)%n] = in.nextInt();
        }
        for(int i = 0; i < n; i++)
            System.out.print(a[i] + " ");
      
        System.out.println();
      
    }
}
          • ngokli + 1 comment

            This is a good reason to start looping on the first element of the input, rather than the output.

            But the problem statement does say you are "Given an array" (not a stream).

            • jacob0306 + 1 comment

              Nah I did not add anything except changed the gived codes from a [a_i] = in.nextInt() to a[((n- (k%n))+a_i)%n] = in.nextInt()

              • adivishy + 0 comments

                can you pl explain a[((n- (k%n))+a_i)%n] = in.nextInt() st

        • hackerrank_com23 + 3 comments

          Here's my in-place function implementation:

          public static int[] arrayLeftRotation(int[] a, int n, int k) {
    // Rotate in-place
    int[] temp = new int[k];
    System.arraycopy(a, 0, temp, 0, k);
    System.arraycopy(a, k, a, 0, n - k);
    System.arraycopy(temp, 0, a, n - k, k);
    return a;
}
          • Angi29 + 0 comments
            [deleted]
          • Angi29 + 0 comments

            idem, just a little variation : kifs

            static int[] rotLeft(int[] a, int d) {
    int length = a.length;
    int[] b = new int[length];

    System.arraycopy(a, d, b, 0, length - d);
    System.arraycopy(a, 0, b, length - d, d);
    return b;
}
          • denis631 + 1 comment

            How is this in-place when you allocate a new array of size k.

            • venom1724 + 0 comments

              Indeed, its not in-place at all. Also its slow. If you are interested, here's an inplace c++ solution 

              void rotLeft(vector<int> &a, int d) {
    int c=a[d],ci=0,n=a.size(); a[d]=0;
    for(int i=n-1;i>=0;i--){
        swap(a[ci],c);
        if(!c&&i) ci+=n-i+++i;
        ci=(n+ci-d)%n;
    }
}
    • mohitgautam2k16 + 0 comments
      [deleted]
    • 123shuklaprasha1 + 0 comments

      why u have used that command of else please explain me

    • cc_insp + 0 comments

      I used the System.arraycopy() method which was used in the video tutorial. I'm wondering if this solution is more efficient or mine?

      import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();
        int a[] = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        a = leftRotation(n, k, a);
        for (int i=0; i<a.length; i++) {
            System.out.print(a[i]+" ");
        }
    }
    public static int[] leftRotation(int n, int k, int[] a){
        int[] copy = new int[n];
        System.arraycopy(a, k, copy, 0, (n - k));
        System.arraycopy(a, 0, copy, (n - k), (n - (n - k)));
        return copy;
    }
}
    • yash_97373 + 0 comments

      Is calculation really required ?

      for(int i=k; i < a.length; i++){
    System.out.print(a[i] + " ");
}
for(int i=0; i < k; i++){
    System.out.print(a[i] + " ");
}
    • arn_pune + 0 comments
      [deleted]