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

1. Reverse words but keep word order intact s = "hello world" print(" ".join(word[::-1] for word in s.split())) # olleh dlrow
2. Check if string has all unique characters (no duplicates) s = "abcdefg" print(len(set(s)) == len(s)) # True
3. 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

4. Find missing letter in a sequence (a-z) import string s = "abcdfgh" missing = set(string.ascii_lowercase) - set(s) print(missing) # {'e', ...}
5. 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
6. 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

7. Extract only digits from a string import re s = "abc123xyz" print("".join(re.findall(r"\d", s))) # '123'
8. Check if string is valid email import re email = "test@example.com" print(bool(re.match(r"^[\w\.-]+@[\w\.-]+\.\w+$", email))) # True
9. Find longest word in sentence s = "Python coding interview preparation" print(max(s.split(), key=len)) # 'preparation'

🔹 Level 4 – Advanced Puzzles

10. 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'

11. Find first recurring character

s = "ABCADEF"
seen = set()
for ch in s:
    if ch in seen:
        print(ch)  # A
        break
    seen.add(ch)

12. 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.