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Group Anagrams

UberSoftware Engineer · Onsite
MediumSoftware EngineerOnsiteCoding & Algorithms

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This problem tests your ability to identify and implement an efficient grouping mechanism using hash maps to categorize strings by a common canonical form.

Problem Statement

Given an array of strings, group the anagrams together. An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Return the answer in any order.

Function Signature

def group_anagrams(strs: list[str]) -> list[list[str]]:

Constraints

  • 1 <= strs.length <= 10^4
  • 0 <= strs[i].length <= 100
  • strs[i] consists of lowercase English letters.

Examples

Example 1: Input: strs = ["eat", "tea", "tan", "ate", "nat", "bat"] Output: [["bat"], ["nat", "tan"], ["ate", "eat", "tea"]]

Example 2: Input: strs = [""] Output: [[""]]

Edge Cases

  • Empty list of strings.
  • Strings with identical characters repeated (e.g., "aa", "a").
  • List containing strings of varying lengths.

Hints

Hint 1

Consider that all anagrams share the same frequency count of each character.

Hint 2

Can you create a unique key for each string that remains consistent regardless of the character order?

Hint 3

A hash map (dictionary) where the key is the canonical representation and the value is a list of original strings will allow for efficient grouping.

Follow-up questions

  • How would your implementation change if you had to handle case-insensitivity (e.g., 'Eat' and 'tea' are anagrams)?
  • If the input strings were extremely long (e.g., 10^6 characters), how would you optimize the canonical key generation?
  • Could you solve this problem if the input was a massive stream of strings that doesn't fit into memory?