Overview
We’ll solve the combinations_with_replacement function, one of the most well-known HackerRank Python challenges that makes use of the itertools library, in this post.
This task teaches you how to handle strings in a sorted fashion and how to create combinations when repetition is permitted.
You can watch my YouTube video to follow along visually as I walk through this issue step-by-step and run the code in real time.
Statement of the Problem
An integer k and a string s are provided to you.
It is your responsibility to print, in lexicographic order, every combination of characters of length k that have been replaced.
Example Input:
HACK 2Example Output:
AA
AC
AH
AK
CC
CH
CK
HH
HK
KKPython – Solution
This is the straightforward HackerRank solution that makes use of Python’s itertools:
from itertools import combinations_with_replacement
s, k = input().strip().split()
for c in combinations_with_replacement(sorted(s), int(k)):
print("".join(c))
Step-by-Step Explanation
Step 1:
Using Python’s itertools, import the modulele HackerRank solution:
from itertools import combinations_with_replacementA built-in Python module called itertools enables us to construct iterators for effective looping.
Combinations_with_replacement(), which creates combinations that permit repeated elements, will be used in this case.
Step 2:
Take input
s, k = input().strip().split()The input comes in a single line (e.g., HACK 2), so we split it into:
s→"HACK"k→"2"(we’ll later convert it to an integer).
Step 3:
Sort the string
sorted(s)Sorting ensures that the output is lexicographically ordered (alphabetically arranged).
Step 4:
Generate combinations
combinations_with_replacement(sorted(s), int(k))This creates every possible combination of length k (with repetition).
Example for "HACK" and k=2:
→ AA, AC, AH, AK, CC, CH, CK, HH, HK, KK
Step 5:
Print formatted output
print("".join(c))Every combination c is a tuple, such as “A” and “C.”
Before printing, we combine it into the string “AC.”
Example Run
Input:
HACK 2Output:
AA
AC
AH
AK
CC
CH
CK
HH
HK
KK
Why This Method Is Effective
- No additional imports are required because it makes use of Python’s standard library.
- It’s short, clean, and efficient.
- Sorting before creating combinations guarantees that your output is already in order, meeting HackerRank’s specifications.
Important Takeaways
For creating recurring combinations, combinations_with_replacement() is an excellent tool.
If lexicographic order is necessary, always sort the input string.
Coding challenges require the ability to read input, process iterables, and print cleanly, all of which are taught by simple problems like this one.
Visit YouTube to View the Complete Solution
Check out my YouTube tutorial, where I run and walk through this exact code in real time, if you want a step-by-step video explanation.
Link: https://youtu.be/4maYUSCBTYE?si=_rJC1q4quMLvQDRm
In just a few lines of code, you can solve the HackerRank “itertools.combinations_with_replacement()” challenge in Python!
It is easy to use and ideal for anyone learning Python’s itertools module.
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