Top 20 Python Interview Questions 2025. Problem 1 With Funny Example

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🔄 1. How to Reverse a String in Python (Without and With Built-in Methods!)

Have you ever wanted to flip words backward, just for fun? Or maybe you’re trying to write a secret code that only people with mirror vision can understand? 🤔

Today, we’ll explore how to reverse a string in Python using different approaches, including without built-in methods and with built-in methods (because Python is awesome). Let’s dive in! 🚀

🛠️ Method 1: Reversing a String WITHOUT Using Built-in Functions

Imagine you’re eating a pizza 🍕, but instead of starting from the front, you decide to eat it backwards from the last slice to the first. That’s exactly what we do in this method!


def reverse_string(s):
    reversed_s = ""  
    for char in s:   
        reversed_s = char + reversed_s  
    return reversed_s  

# Example Usage
word = "PIZZA"
reversed_word = reverse_string(word)
print(f"Original: {word} -> Reversed: {reversed_word}")

🔍 Explanation (Step-by-step)

  • Step 1: Define the function reverse_string(s).
  • Step 2: Create an empty string reversed_s to store the reversed string.
  • Step 3: Loop through each character in s.
  • Step 4: Prepend the character to reversed_s, building the string backwards.
  • Step 5: Return the reversed string.

Example Walkthrough:

Step Character Reversed String
1'P'"P"
2'I'"IP"
3'Z'"ZIP"
4'Z'"ZZIP"
5'A'"AZZIP"

✅ Method 2: Reversing a String Using Python’s [::-1] Slicing

Python is so cool, it can reverse a string with just one line of code! 😎


def reverse_string_slice(s):
    return s[::-1]  

word = "PYTHON"
reversed_word = reverse_string_slice(word)
print(f"Original: {word} -> Reversed: {reversed_word}")

🔍 Explanation:

s[::-1] means:

  • : → Take everything
  • : → Take everything (again)
  • -1 → Step backward, so it reads the string in reverse order

✅ Method 3: Reversing a String Using .reverse() (for Lists)

This method works by converting the string into a list, reversing it, and then joining it back into a string.


def reverse_string_list(s):
    char_list = list(s)  
    char_list.reverse()  
    return ''.join(char_list)  

word = "PYTHON"
reversed_word = reverse_string_list(word)
print(f"Original: {word} -> Reversed: {reversed_word}")

🔍 Explanation:

  • Convert the string into a list of characters: list(s).
  • Use .reverse() to flip the list.
  • Join it back into a string using ''.join().

🏆 Conclusion: Which Method is Best?

Method Pros Cons
Manual Loop Good for learning Not the most efficient
Slicing [::-1] Super fast & clean Might look confusing at first
List .reverse() Uses built-in methods Needs conversion

Each method has its own advantages, but if you're looking for the quickest way, s[::-1] is the best. 🚀

Give it a try and see what fun words you can reverse! 🔹 What does your name look like backwards? Try it in the comments! 😆

python-interview-coding-2-with-funny-example


Top 20 Python Coding Interview Questions

Here are the 20 most common Python coding interview questions asked in technical interviews:

  1. Reverse a string - Write a function to reverse a string without using built-in reverse functions.

  2. Check for palindrome - Determine if a given string is a palindrome (reads the same backward as forward).

  3. Find missing number - Given an array containing n distinct numbers taken from 0 to n, find the missing number.

  4. Two Sum problem - Find pairs in an array that sum to a target value.

  5. String anagram check - Determine if two strings are anagrams of each other.

  6. Find duplicate elements - Find all duplicates in an array with O(n) time complexity.

  7. Binary search implementation - Write a function to perform binary search on a sorted array.

  8. Fibonacci sequence - Generate the Fibonacci sequence up to n terms.

  9. Linked list cycle detection - Detect if a linked list has a cycle using Floyd's Tortoise and Hare algorithm.

  10. Implement a stack using queues - Build a stack data structure using queue operations.

  11. Sort a dictionary by values - Write code to sort a dictionary by its values.

  12. Find the longest substring without repeating characters - Return the length of the longest substring without repeating characters.

  13. Implement a binary tree and its traversals - Create a binary tree class with inorder, preorder, and postorder traversals.

  14. Count occurrences of each element - Count the frequency of each element in a list.

  15. Merge two sorted arrays - Combine two sorted arrays into a single sorted array.

  16. Implement a decorator - Create a simple decorator that measures function execution time.

  17. LRU Cache implementation - Design and implement a Least Recently Used (LRU) cache.

  18. Generate all permutations of a string - Write a function to generate all possible permutations of a string.

  19. Find the first non-repeating character - Locate the first non-repeating character in a string.

  20. Level order traversal of a binary tree - Perform breadth-first traversal of a binary tree.

These questions assess algorithmic thinking, data structure knowledge, and Python-specific concepts that are particularly valued in the Indian tech industry. Companies like Amazon, Microsoft, Google, and many Indian startups commonly use these problems during their interview processes.

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