PPractick

The problem

A word game awards points when a player rearranges all the letters of one word into another, like "listen" → "silent". The validator must decide whether two strings are anagrams: exactly the same letters with exactly the same counts, in any order. Sorting both strings and comparing works in O(n log n), but because the alphabet is small, a frequency count does it in O(n): add one for each letter of the first string, subtract one for each letter of the second, and check that everything cancels out.

Example: ("anagram", "nagaram") → true; ("rat", "car") → false.

Function signature

bool isAnagram(const string& s, const string& t);  // lowercase English letters

Test cases

Input (s, t)	Output	Explanation
("anagram", "nagaram")	true	Same letters, same counts
("rat", "car")	false	t has a c, s has a t
("a", "ab")	false	Different lengths
("", "")	true
("aacc", "ccac")	false	a appears twice in s but once in t
("listen", "silent")	true

(Confirm: lowercase English letters only; a Unicode version would use a hash map instead of an array.)

How interviewers phrase it

• "Check whether two strings are anagrams" (LeetCode 242).
• Follow-ups: group anagrams (LeetCode 49), find all anagram positions of a pattern in a text (LeetCode 438).

Clarifying questions to ask

1. Which characters: lowercase letters, ASCII, or Unicode?
2. Case-sensitive? Do spaces count?
3. How long are the strings?

Follow-ups to expect

1. "Sorting or counting?"
2. "How would you handle Unicode?"
3. "How would you group many words into anagram sets?"
4. "How do you find anagrams of a pattern inside a long text?"
5. "Complexity?"

Related questions

• Sort Characters by Frequency Easy
• Isomorphic String Easy
• Replace Elements by Their Rank Easy
• Roman to Integer Medium
• Sum of Beauty of All Substrings Medium
• Longest Repeating Character Replacement Hard

All 474 dsa interview questions

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