Python Program to replace list elements within a range with a given number

Given a range, the task here  is to write a python program that can update the list elements falling under a given index range with a specified number.

Input : test_list = [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1], i, j = 4, 8, K = 9

Output : [4, 6, 8, 1, 9, 9, 9, 9, 12, 3, 9, 1]

Explanation : List is updated with 9 from 4th to 8th index.

Input : test_list = [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1], i, j = 4, 8, K = 8

Output : [4, 6, 8, 1, 8, 8, 8, 8, 12, 3, 9, 1]

Explanation : List is updated with 8 from 4th to 8th index.

Method 1 : Using slicing and * operator

In this, we perform task of getting elements of range using slicing and * operator is used to perform update and provide required elements to fill updates.

Program:

Python3

# initializing list
test_list = [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1]

# printing original list
print("The original list is : " + str(test_list))

# initializing i, j
i, j = 4, 8

# initializing K
K = 9

# getting range using slicing and
# required elements using * operator
test_list[i:j] = [K] * (j - i)

# printing result
print("Range Updated list : " + str(test_list))

Output:

The original list is : [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1]

Range Updated list : [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1, 9]

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

Method 2 : Using repeat() and list slicing

The similar task can also be performed using repeat(), which uses unbuilt constructs to get required elements.

Program:

Python3

from itertools import repeat

# initializing list
test_list = [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1]

# printing original list
print("The original list is : " + str(test_list))

# initializing i, j
i, j = 4, 8

# initializing K
K = 9

# getting range using slicing and
# required elements using repeat()
test_list[i:j] = repeat(K, (j - i))

# printing result
print("Range Updated list : " + str(test_list))

Output:

The original list is : [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1]

Range Updated list : [4, 6, 8, 1, 2, 9, 0, 10, 12, 3, 9, 1, 9]

Time Complexity: O(n) where n is the number of elements in the list “test_list”. The repeat() and list slicing is used to perform the task and it takes O(n) time.
Auxiliary Space: O(1) additional space not required