Hello Everyone,
Questions: Write a function rotate(ar[], d, n) that rotates arr[] of size n by d elements.
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;
/*Prototype for utility functions */
void
printArray(
int
arr[],
int
size);
void
swap(
int
arr[],
int
fi,
int
si,
int
d);
void
leftRotate(
int
arr[],
int
d,
int
n)
{
/* Return If number of elements to be rotated
is zero or equal to array size */
if
(d == 0 || d == n)
return
;
/*If number of elements to be rotated
is exactly half of array size */
if
(n - d == d)
{
swap(arr, 0, n - d, d);
return
;
}
/* If A is shorter*/
if
(d < n - d)
{
swap(arr, 0, n - d, d);
leftRotate(arr, d, n - d);
}
else
/* If B is shorter*/
{
swap(arr, 0, d, n - d);
leftRotate(arr + n - d, 2 * d - n, d);
/*This is tricky*/
}
}
/*UTILITY FUNCTIONS*/
/* function to print an array */
void
printArray(
int
arr[],
int
size)
{
int
i;
for
(i = 0; i < size; i++)
cout << arr[i] <<
" "
;
cout << endl;
}
/*This function swaps d elements starting at index fi
with d elements starting at index si */
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;
}
}
// Driver Code
int
main()
{
int
arr[] = {1, 2, 3, 4, 5, 6, 7};
leftRotate(arr, 2, 7);
printArray(arr, 7);
return
0;
}
// This code is contributed by rathbhupendra
Output:
3 5 4 6 7 1 2
Iterative Implementation:
Here is iterative implementation of the same algorithm. Same utility function swap() is used here.
- C
void
leftRotate(
int
arr[],
int
d,
int
n)
{
int
i, j;
if
(d == 0 || d == n)
return
;
i = d;
j = n - d;
while
(i != j)
{
if
(i < j)
/*A is shorter*/
{
swap(arr, d-i, d+j-i, i);
j -= i;
}
else
/*B is shorter*/
{
swap(arr, d-i, d, j);
i -= j;
}
// printArray(arr, 7);
}
/*Finally, block swap A and B*/
swap(arr, d-i, d, i);
}
Time Complexity: O(n)