Awesome 😃 — let’s go beyond the basics and collect the tricky, puzzle-style string interview questions that often catch candidates off guard.
🧩 Tricky String Interview Questions (Puzzle Style)
🔹 Level 1 – Edge-Case Fundamentals
- Reverse words but keep word order intact
s = "hello world" print(" ".join(word[::-1] for word in s.split())) # olleh dlrow - Check if string has all unique characters (no duplicates)
s = "abcdefg" print(len(set(s)) == len(s)) # True - Check if two strings are isomorphic
(each char in s1 can be mapped to a unique char in s2)def is_isomorphic(s1, s2): return len(set(zip(s1, s2))) == len(set(s1)) == len(set(s2)) print(is_isomorphic("egg","add")) # True print(is_isomorphic("foo","bar")) # False
🔹 Level 2 – ASCII / Encoding Based
- Find missing letter in a sequence (a-z)
import string s = "abcdfgh" missing = set(string.ascii_lowercase) - set(s) print(missing) # {'e', ...} - Check if string is pangram (contains all alphabets)
import string s = "The quick brown fox jumps over a lazy dog" print(set(string.ascii_lowercase).issubset(s.lower())) # True - Caesar Cipher (shift characters by 3)
s = "abc" shift = 3 encrypted = "".join(chr((ord(c)-97+shift)%26 + 97) for c in s) print(encrypted) # def
🔹 Level 3 – Regex / Pattern Matching
- Extract only digits from a string
import re s = "abc123xyz" print("".join(re.findall(r"\d", s))) # '123' - Check if string is valid email
import re email = "test@example.com" print(bool(re.match(r"^[\w\.-]+@[\w\.-]+\.\w+$", email))) # True - Find longest word in sentence
s = "Python coding interview preparation" print(max(s.split(), key=len)) # 'preparation'
🔹 Level 4 – Advanced Puzzles
- Longest palindrome substring (DP or expand-around-center)
def longest_palindrome(s):
res = ""
for i in range(len(s)):
for j in (0,1): # odd/even
l, r = i, i+j
while l>=0 and r<len(s) and s[l]==s[r]:
if r-l+1 > len(res):
res = s[l:r+1]
l -= 1; r += 1
return res
print(longest_palindrome("babad")) # 'bab' or 'aba'
- Find first recurring character
s = "ABCADEF"
seen = set()
for ch in s:
if ch in seen:
print(ch) # A
break
seen.add(ch)
- Group anagrams together
from collections import defaultdict
strs = ["eat","tea","tan","ate","nat","bat"]
d = defaultdict(list)
for word in strs:
d["".join(sorted(word))].append(word)
print(list(d.values()))
# [['eat','tea','ate'], ['tan','nat'], ['bat']]
✅ These are the “tricky string problems” companies like Amazon, Microsoft, and product startups love to ask.