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Python Program for array rotation
  • Difficulty Level : Medium
  • Last Updated : 04 Mar, 2021

Write a function rotate(ar[], d, n) that rotates arr[] of size n by d elements. 

Array

Rotation of the above array by 2 will make array

ArrayRotation1

METHOD 1 (Using temp array):



Input arr[] = [1, 2, 3, 4, 5, 6, 7], d = 2, n =7
1) Store d elements in a temp array
   temp[] = [1, 2]
2) Shift rest of the arr[]
   arr[] = [3, 4, 5, 6, 7, 6, 7]
3) Store back the d elements
   arr[] = [3, 4, 5, 6, 7, 1, 2]

Python3




# function to rotate array by d elements using temp array
def rotateArray(arr, n, d):
    temp = []
    i = 0
    while (i < d):
        temp.append(arr[i])
        i = i + 1
    i = 0
    while (d < n):
        arr[i] = arr[d]
        i = i + 1
        d = d + 1
    arr[:] = arr[: i] + temp
    return arr
 
 
# Driver function to test above function
arr = [1, 2, 3, 4, 5, 6, 7]
print("Array after left rotation is: ", end=' ')
print(rotateArray(arr, len(arr), 2))
 
# this code is contributed by Anabhra Tyagi


Output

Array after left rotation is:  [3, 4, 5, 6, 7, 1, 2]

Time complexity: O(n) 
Auxiliary Space: O(d)

METHOD 2 (Rotate one by one) : 

leftRotate(arr[], d, n)
start
  For i = 0 to i < d
    Left rotate all elements of arr[] by one
end

To rotate by one, store arr[0] in a temporary variable temp, move arr[1] to arr[0], arr[2] to arr[1] …and finally temp to arr[n-1]
Let us take the same example arr[] = [1, 2, 3, 4, 5, 6, 7], d = 2 
Rotate arr[] by one 2 times 
We get [2, 3, 4, 5, 6, 7, 1] after first rotation and [ 3, 4, 5, 6, 7, 1, 2] after second rotation. 

Python3




#Function to left rotate arr[] of size n by d*/
def leftRotate(arr, d, n):
    for i in range(d):
        leftRotatebyOne(arr, n)
 
#Function to left Rotate arr[] of size n by 1*/
def leftRotatebyOne(arr, n):
    temp = arr[0]
    for i in range(n-1):
        arr[i] = arr[i+1]
    arr[n-1] = temp
         
 
# utility function to print an array */
def printArray(arr,size):
    for i in range(size):
        print ("%d"% arr[i],end=" ")
 
  
# Driver program to test above functions */
arr = [1, 2, 3, 4, 5, 6, 7]
leftRotate(arr, 2, 7)
printArray(arr, 7)
 
# This code is contributed by Shreyanshi Arun


Output

3 4 5 6 7 1 2 

Time complexity : O(n * d) 
Auxiliary Space : O(1) 

METHOD 3 (A Juggling Algorithm) 
This is an extension of method 2. Instead of moving one by one, divide the array in different sets 
where number of sets is equal to GCD of n and d and move the elements within sets. 
If GCD is 1 as is for the above example array (n = 7 and d =2), then elements will be moved within one set only, we just start with temp = arr[0] and keep moving arr[I+d] to arr[I] and finally store temp at the right place.
Here is an example for n =12 and d = 3. GCD is 3 and 

Let arr[] be {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}

a)    Elements are first moved in first set – (See below diagram for this movement

ArrayRotation

          arr[] after this step --> {4 2 3 7 5 6 10 8 9 1 11 12}

b)    Then in second set.
          arr[] after this step --> {4 5 3 7 8 6 10 11 9 1 2 12}

c)    Finally in third set.
          arr[] after this step --> {4 5 6 7 8 9 10 11 12 1 2 3}

Python3




#Function to left rotate arr[] of size n by d
def leftRotate(arr, d, n):
    for i in range(gcd(d,n)):
         
        # move i-th values of blocks
        temp = arr[i]
        j = i
        while 1:
            k = j + d
            if k >= n:
                k = k - n
            if k == i:
                break
            arr[j] = arr[k]
            j = k
        arr[j] = temp
 
#UTILITY FUNCTIONS
#function to print an array
def printArray(arr, size):
    for i in range(size):
        print ("%d" % arr[i], end=" ")
  
#Function to get gcd of a and b
def gcd(a, b):
    if b == 0:
        return a;
    else:
        return gcd(b, a%b)
  
# Driver program to test above functions
arr = [1, 2, 3, 4, 5, 6, 7]
leftRotate(arr, 2, 7)
printArray(arr, 7)
 
# This code is contributed by Shreyanshi Arun


Output

3 4 5 6 7 1 2 

Time complexity : O(n) 
Auxiliary Space : O(1)

Another Approach : Using List slicing

Python3




# Python program using the List
# slicing approch to rotate the array
def rotateList(arr,d,n):
  arr[:]=arr[d:n]+arr[0:d]
  return arr
# Driver function to test above function
arr = [1, 2, 3, 4, 5, 6]
print(arr)
print("Rotated list is")
print(rotateList(arr,2,len(arr))) 
 
# this code is contributed by virusbuddah


Output

[1, 2, 3, 4, 5, 6]
Rotated list is
[3, 4, 5, 6, 1, 2]

Please refer complete article on Program for array rotation for more details!

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