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Python program to right rotate a list by n

  • Difficulty Level : Easy
  • Last Updated : 21 Nov, 2018

Given a list, right rotate the list by n position.

Examples :

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Input : n = 2 
         List_1 = [1, 2, 3, 4, 5, 6]
Output : List_1 = [5, 6, 1, 2, 3, 4]
We get output list after right rotating 
(clockwise) given list by 2.

Input :  n = 3
         List_1 = [3, 0, 1, 4, 2, 3]
Output : List_1 = [4, 2, 3, 3, 0, 1]

Approach #1 : Traverse the first list one by one and then put the elements at required places in a second list.






# Python program to right rotate a list by n
  
# Returns the rotated list
def rightRotate(lists, num):
    output_list = []
      
    # Will add values from n to the new list
    for item in range(len(lists) - num, len(lists)):
        output_list.append(lists[item])
      
    # Will add the values before
    # n to the end of new list    
    for item in range(0, len(lists) - num): 
        output_list.append(lists[item])
          
    return output_list
  
# Driver Code
rotate_num = 3
list_1 = [1, 2, 3, 4, 5, 6]
  
print(rightRotate(list_1, rotate_num))

Output :

[4, 5, 6, 1, 2, 3]

Time complexity : O(n)
 

Approach #2 : Another approach to solve this problem by using slicing technique. One way of slicing list is by using len() method.




# Python program to right rotate 
# a list by n using list slicing
n = 3
  
list_1 = [1, 2, 3, 4, 5, 6]
list_1 = (list_1[len(list_1) - n:len(list_1)] 
                 + list_1[0:len(list_1) - n])
print(list_1)

Output:

[4, 5, 6, 1, 2, 3]

 
Approach #3 : In the above method, last n elements of list_1 was taken and then remaining elements of list_1. Another way is without using len() method.




# Right Rotating a list to n positions
n = 3
  
list_1 = [1, 2, 3, 4, 5, 6]
list_1 = (list_1[-n:] + list_1[:-n])
  
print(list_1)

Output :

[4, 5, 6, 1, 2, 3]

Time complexity : O(n)
 
Note : list_1[:] will return the whole list as the blank space on left of slicing operator refers to start of list i.e 0 and blank space on right refers to ending position of list.




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