Block swap algorithm for array rotation
Write a function rotate(arr[], d, n) that rotates arr[] of size n by d elements.
Rotation of the above array by 2 will make an array
Algorithm :
Initialize A = arr[0..d-1] and B = arr[d..n-1]
1) Do following until size of A is equal to size of B
a) If A is shorter, divide B into Bl and Br such that Br is of same
length as A. Swap A and Br to change ABlBr into BrBlA. Now A
is at its final place, so recur on pieces of B.
b) If A is longer, divide A into Al and Ar such that Al is of same
length as B Swap Al and B to change AlArB into BArAl. Now B
is at its final place, so recur on pieces of A.
2) Finally when A and B are of equal size, block swap them.
Recursive Implementation:
C++
#include <bits/stdc++.h>
using namespace std;
#include <bits/stdc++.h>
using namespace std;
void printArray( int arr[], int size)
{
int i;
for (i = 0; i < size; i++)
cout << arr[i] << " " ;
cout << endl;
}
void swap( int arr[], int fi, int si, int d)
{
int i, temp;
for (i = 0; i < d; i++) {
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
void leftRotate( int arr[], int d, int n)
{
if (d == 0 || d == n)
return ;
if (d > n)
d = d % n;
if (n - d == d) {
swap(arr, 0, n - d, d);
return ;
}
if (d < n - d) {
swap(arr, 0, n - d, d);
leftRotate(arr, d, n - d);
}
else
{
swap(arr, 0, d, n - d);
leftRotate(arr + n - d, 2 * d - n,
d);
}
}
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
leftRotate(arr, 2, 7);
printArray(arr, 7);
return 0;
}
|
C
#include<stdio.h>
void printArray( int arr[], int size);
void swap( int arr[], int fi, int si, int d);
void leftRotate( int arr[], int d, int n)
{
if (d == 0 || d == n)
return ;
if (n-d == d)
{
swap(arr, 0, n-d, d);
return ;
}
if (d < n-d)
{
swap(arr, 0, n-d, d);
leftRotate(arr, d, n-d);
}
else
{
swap(arr, 0, d, n-d);
leftRotate(arr+n-d, 2*d-n, d);
}
}
void printArray( int arr[], int size)
{
int i;
for (i = 0; i < size; i++)
printf ( "%d " , arr[i]);
printf ( "\n " );
}
void swap( int arr[], int fi, int si, int d)
{
int i, temp;
for (i = 0; i<d; i++)
{
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
int main()
{
int arr[] = {1, 2, 3, 4, 5, 6, 7};
leftRotate(arr, 2, 7);
printArray(arr, 7);
getchar ();
return 0;
}
|
Java
import java.util.*;
class GFG
{
public static void leftRotate( int arr[], int d,
int n)
{
leftRotateRec(arr, 0 , d, n);
}
public static void leftRotateRec( int arr[], int i,
int d, int n)
{
if (d == 0 || d == n)
return ;
if (n - d == d)
{
swap(arr, i, n - d + i, d);
return ;
}
if (d < n - d)
{
swap(arr, i, n - d + i, d);
leftRotateRec(arr, i, d, n - d);
}
else
{
swap(arr, i, d, n - d);
leftRotateRec(arr, n - d + i, 2 * d - n, d);
}
}
public static void printArray( int arr[], int size)
{
int i;
for (i = 0 ; i < size; i++)
System.out.print(arr[i] + " " );
System.out.println();
}
public static void swap( int arr[], int fi,
int si, int d)
{
int i, temp;
for (i = 0 ; i < d; i++)
{
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
public static void main (String[] args)
{
int arr[] = { 1 , 2 , 3 , 4 , 5 , 6 , 7 };
leftRotate(arr, 2 , 7 );
printArray(arr, 7 );
}
}
|
Python3
def leftRotate(arr, d, n):
leftRotateRec(arr, 0 , d, n);
def leftRotateRec(arr, i, d, n):
if (d = = 0 or d = = n):
return ;
if (n - d = = d):
swap(arr, i, n - d + i, d);
return ;
if (d < n - d):
swap(arr, i, n - d + i, d);
leftRotateRec(arr, i, d, n - d);
else :
swap(arr, i, d, n - d);
leftRotateRec(arr, n - d + i, 2 * d - n, d);
def printArray(arr, size):
for i in range (size):
print (arr[i], end = " " );
print ();
def swap(arr, fi, si, d):
for i in range (d):
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
if __name__ = = '__main__' :
arr = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ];
leftRotate(arr, 2 , 7 );
printArray(arr, 7 );
|
C#
using System;
class GFG{
public static void leftRotate( int []arr,
int d, int n)
{
leftRotateRec(arr, 0, d, n);
}
public static void leftRotateRec( int []arr, int i,
int d, int n)
{
if (d == 0 || d == n)
return ;
if (n - d == d)
{
swap(arr, i, n - d + i, d);
return ;
}
if (d < n - d)
{
swap(arr, i, n - d + i, d);
leftRotateRec(arr, i, d, n - d);
}
else
{
swap(arr, i, d, n - d);
leftRotateRec(arr, n - d + i,
2 * d - n, d);
}
}
public static void printArray( int []arr,
int size)
{
int i;
for (i = 0; i < size; i++)
Console.Write(arr[i] + " " );
Console.WriteLine();
}
public static void swap( int []arr, int fi,
int si, int d)
{
int i, temp;
for (i = 0; i < d; i++)
{
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
public static void Main(String[] args)
{
int []arr = { 1, 2, 3, 4, 5, 6, 7 };
leftRotate(arr, 2, 7);
printArray(arr, 7);
}
}
|
Javascript
<script>
let leftRotate = (arr, d, n) =>{
if (d == 0 || d == n)
return ;
if (n - d == d) {
arr = swap(arr, 0, n - d, d);
return ;
}
if (d < n - d) {
arr = swap(arr, 0, n - d, d);
leftRotate(arr, d, n - d);
}
else {
arr = swap(arr, 0, d, n - d);
leftRotate(arr + n - d, 2 * d - n, d);
}
}
let printArray = (arr, size) =>{
ans = ''
for (let i = 0; i < size; i++)
ans += arr[i]+ " " ;
document.write(ans)
}
let swap = (arr, fi, si, d) =>{
for (let i = 0; i < d; i++) {
let temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
return arr
}
arr = [1, 2, 3, 4, 5, 6, 7];
leftRotate(arr, 2, 7);
printArray(arr, 7);
</script>
|
Time Complexity: O(n)
Auxiliary Space: O(log n)
Iterative Implementation:
Here is an iterative implementation of the same algorithm. The same utility function swap() is used here.
C++
#include <bits/stdc++.h>
using namespace std;
void printArray( int arr[], int size)
{
int i;
for (i = 0; i < size; i++)
cout << arr[i] << " " ;
cout << endl;
}
void swap( int arr[], int fi, int si, int d)
{
int i, temp;
for (i = 0; i < d; i++) {
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
void leftRotate( int arr[], int d, int n)
{
int i, j;
if (d == 0 || d == n)
return ;
if (d > n)
d = d % n;
i = d;
j = n - d;
while (i != j) {
if (i < j)
{
swap(arr, d - i, d + j - i, i);
j -= i;
}
else
{
swap(arr, d - i, d, j);
i -= j;
}
}
swap(arr, d - i, d, i);
}
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
leftRotate(arr, 2, 7);
printArray(arr, 7);
return 0;
}
|
C
#include <stdio.h>
void printArray( int arr[], int size)
{
int i;
for (i = 0; i < size; i++)
printf ( "%d " , arr[i]);
printf ( "\n " );
}
void swap( int arr[], int fi, int si, int d)
{
int i, temp;
for (i = 0; i < d; i++) {
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
void leftRotate( int arr[], int d, int n)
{
int i, j;
if (d == 0 || d == n)
return ;
if (d > n)
d = d % n;
i = d;
j = n - d;
while (i != j) {
if (i < j)
{
swap(arr, d - i, d + j - i, i);
j -= i;
}
else
{
swap(arr, d - i, d, j);
i -= j;
}
}
swap(arr, d - i, d, i);
}
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
leftRotate(arr, 2, 7);
printArray(arr, 7);
getchar ();
return 0;
}
|
Java
import java.io.*;
public class GFG {
static void leftRotate( int arr[], int d, int n)
{
int i, j;
if (d == 0 || d == n)
return ;
if (d > n)
d = d % n;
i = d;
j = n - d;
while (i != j) {
if (i < j)
{
swap(arr, d - i, d + j - i, i);
j -= i;
}
else
{
swap(arr, d - i, d, j);
i -= j;
}
}
swap(arr, d - i, d, i);
}
public static void printArray( int arr[], int size)
{
int i;
for (i = 0 ; i < size; i++)
System.out.print(arr[i] + " " );
System.out.println();
}
public static void swap( int arr[], int fi, int si,
int d)
{
int i, temp;
for (i = 0 ; i < d; i++) {
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
public static void main(String[] args)
{
int arr[] = { 1 , 2 , 3 , 4 , 5 , 6 , 7 };
leftRotate(arr, 2 , 7 );
printArray(arr, 7 );
}
}
|
Python3
def printArray(arr, size):
for i in range (size):
print (arr[i], end = " " )
print ()
def swap(arr, fi, si, d):
for i in range (d):
temp = arr[fi + i]
arr[fi + i] = arr[si + i]
arr[si + i] = temp
def leftRotate(arr, d, n):
if (d = = 0 or d = = n):
return
i = d
j = n - d
while (i ! = j):
if (i < j):
swap(arr, d - i, d + j - i, i)
j - = i
else :
swap(arr, d - i, d, j)
i - = j
swap(arr, d - i, d, i)
if __name__ = = '__main__' :
arr = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]
leftRotate(arr, 2 , 7 )
printArray(arr, 7 )
|
C#
using System;
class GFG {
public static void printArray( int [] arr, int size)
{
int i;
for (i = 0; i < size; i++)
Console.Write(arr[i] + " " );
Console.WriteLine();
}
public static void swap( int [] arr, int fi, int si,
int d)
{
int i, temp;
for (i = 0; i < d; i++) {
temp = arr[fi + i];
arr[fi + i] = arr[si + i];
arr[si + i] = temp;
}
}
static void leftRotate( int [] arr, int d, int n)
{
int i, j;
if (d == 0 || d == n)
return ;
if (d > n)
d = d % n;
i = d;
j = n - d;
while (i != j) {
if (i < j)
{
swap(arr, d - i, d + j - i, i);
j -= i;
}
else
{
swap(arr, d - i, d, j);
i -= j;
}
}
swap(arr, d - i, d, i);
}
public static void Main(String[] args)
{
int [] arr = { 1, 2, 3, 4, 5, 6, 7 };
leftRotate(arr, 2, 7);
printArray(arr, 7);
}
}
|
Javascript
<script>
function leftRotate(arr, d, n)
{
if (d == 0 || d == n)
return ;
let i = d;
let j = n - d;
while (i != j)
{
if (i < j)
{
arr = swap(arr, d - i, d + j - i, i);
j -= i;
}
else {
arr = swap(arr, d - i, d, j);
i -= j;
}
}
arr = swap(arr, d - i, d, i);
}
</script>
|
Time Complexity: O(n)
Auxiliary Space: O(1)
Please see the following posts for other methods of array rotation:
https://www.geeksforgeeks.org/array-rotation/
https://www.geeksforgeeks.org/program-for-array-rotation-continued-reversal-algorithm/
Please write comments if you find any bug in the above programs/algorithms or want to share any additional information about the block swap algorithm.
Last Updated :
20 Jul, 2023
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