Python program to replace first 'K' elements by 'N'

When it is required to replace first 'K' elements by 'N', a simple iteration is used. This operation modifies the original list by substituting the first K elements with a specified value N.

Basic Approach Using Loop

The simplest method uses a for loop with range() to iterate through the first K positions ?

my_list = [13, 34, 26, 58, 14, 32, 16, 89]

print("The list is :")
print(my_list)

K = 2
print("The value of K is :")
print(K)

N = 99
print("The value of N is :")
print(N)

for index in range(K):
    my_list[index] = N

print("The result is :")
print(my_list)

The list is :
[13, 34, 26, 58, 14, 32, 16, 89]
The value of K is :
2
The value of N is :
99
The result is :
[99, 99, 26, 58, 14, 32, 16, 89]

Using List Slicing

An alternative approach uses list slicing to replace multiple elements at once ?

numbers = [13, 34, 26, 58, 14, 32, 16, 89]
K = 3
N = 50

print("Original list:", numbers)
numbers[:K] = [N] * K
print("After replacing first", K, "elements with", N, ":", numbers)

Original list: [13, 34, 26, 58, 14, 32, 16, 89]
After replacing first 3 elements with 50 : [50, 50, 50, 58, 14, 32, 16, 89]

How It Works

• A list of integers is defined and displayed on the console.

• The value for 'K' (number of elements to replace) and 'N' (replacement value) are defined.

• The range(K) generates indices from 0 to K-1.

• Each element at these positions is assigned the value N.

• The slicing method [:K] = [N] * K replaces the first K elements in one operation.

Comparison

Conclusion

Both methods effectively replace the first K elements with value N. The loop approach is more readable for beginners, while slicing offers a more concise solution for experienced programmers.