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💪 Interview Prep

Python Coding Challenges – Interview Problems

Technical interviews test algorithmic problem-solving under pressure. Practice these common Python challenges to build pattern recognition.

⏱️ 20 min read🎯 Interview Prep📅 Updated 2026

Two Sum (Hash Map)

Python
# O(n) time, O(n) space
def two_sum(nums: list[int], target: int) -> list[int]:
    seen = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i
    return []

print(two_sum([2, 7, 11, 15], 9))  # [0, 1]

Valid Palindrome (Two Pointers)

Python
def is_palindrome(s: str) -> bool:
    left, right = 0, len(s) - 1
    while left < right:
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1
        if s[left].lower() != s[right].lower():
            return False
        left += 1; right -= 1
    return True

print(is_palindrome("A man, a plan, a canal: Panama"))  # True

Fibonacci (Dynamic Programming)

Python
# Bottom-up DP: O(n) time, O(1) space
def fib(n):
    if n <= 1: return n
    a, b = 0, 1
    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

# Memoization with lru_cache
from functools import lru_cache
@lru_cache(maxsize=None)
def fib_memo(n):
    if n <= 1: return n
    return fib_memo(n-1) + fib_memo(n-2)

print(fib(10))  # 55
Python
def binary_search(nums: list[int], target: int) -> int:
    left, right = 0, len(nums) - 1
    while left <= right:
        mid = (left + right) // 2
        if nums[mid] == target:
            return mid
        elif nums[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return -1

print(binary_search([1, 3, 5, 7, 9], 7))  # 3

Valid Anagram

Python
from collections import Counter

def is_anagram(s: str, t: str) -> bool:
    return Counter(s) == Counter(t)

print(is_anagram("anagram", "nagaram"))  # True
print(is_anagram("rat", "car"))          # False
Tip: Most interview problems follow 14 patterns: sliding window, two pointers, binary search, tree BFS/DFS, dynamic programming. Practice recognizing patterns, not memorizing solutions.
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