How do you solve Group Anagrams on LeetCode?

Group Anagrams (LeetCode #49) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n * k log k) time complexity and O(n) space complexity. Key insight: Anagrams can be identified by sorting their characters.

What is the brute force solution for Group Anagrams?

The brute force approach for Group Anagrams is Brute Force, with O(n² * k log k) time complexity and O(1) space complexity. The brute force approach involves checking each string against every other string to see if they are anagrams. This is straightforward but inefficient for larger inputs. The optimal Optimal Solution approach improves this to O(n * k log k).

What algorithm or data structure is used to solve Group Anagrams?

Group Anagrams uses the following concepts: Array, Hash Table, String, Sorting. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Group Anagrams?

Always clarify the input constraints and edge cases. Think about space vs. time trade-offs when choosing data structures. Explain your thought process clearly while coding.

What are common mistakes when solving Group Anagrams?

Not considering empty strings or single-character strings. Forgetting to handle case sensitivity or character sets beyond lowercase letters.

#49

Group Anagrams

Medium

ArrayHash TableStringSortingHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n² * k log k)	O(n * k log k)
Space	O(1)	O(n)

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Intuition

Time O(n * k log k)Space O(n)

The optimal solution uses a hash table to group anagrams by their sorted string representation. This way, we can efficiently categorize anagrams without comparing each string directly.

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Algorithm

3 steps

1Step 1: Create a hash map to store groups of anagrams, using the sorted string as the key.
2Step 2: For each string, sort it and use the sorted string as the key to group the original strings.
3Step 3: Collect all groups from the hash map into a list and return it.

solution.py8 lines

1from collections import defaultdict
2
3def groupAnagrams(strs):
4    anagrams = defaultdict(list)
5    for s in strs:
6        key = ''.join(sorted(s))
7        anagrams[key].append(s)
8    return list(anagrams.values())

ℹ

Complexity note: The time complexity is O(n * k log k) because we sort each string (O(k log k)) and do this for n strings. The space complexity is O(n) for storing the grouped anagrams.

1Anagrams can be identified by sorting their characters.
2Using a hash map allows for efficient grouping of anagrams.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.