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Arrays: Left Rotation

  • 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;
    }
}