Group Anagrams - Visual Solution & Python Code

Why it works

Comparing every pair of words is O(n²). The fingerprint collapses the comparison to a dictionary lookup: one pass to bucket, then the answer falls out of the map. Sorting keys costs O(k log k) per word; the letter-count key makes it O(k).

The problem

Given an array of strings, group the anagrams together. You can return the answer in any order. An anagram is a word formed by rearranging the letters of another word.

Hints

• Two strings are anagrams if and only if their sorted characters are identical.
• Use sorted(word) as a dictionary key (convert to tuple for hashability).
• defaultdict(list) makes grouping clean.

Test cases

Reference starter code

from collections import defaultdict

def group_anagrams(strs):
    # Key insight: anagrams have the same sorted characters
    pass

print(group_anagrams(["eat","tea","tan","ate","nat","bat"]))
print(group_anagrams([""]))   # [[""]]
print(group_anagrams(["a"]))  # [["a"]]

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