How do you solve Longest Word in Dictionary on LeetCode?

Longest Word in Dictionary (LeetCode #720) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n log n) time complexity and O(n) space complexity. Key insight: Sorting the words helps in checking prefixes in lexicographical order.

What is the time complexity of Longest Word in Dictionary?

The optimal solution for Longest Word in Dictionary runs in O(n log n) time and uses O(n) space. The time complexity is O(n log n) due to the sorting step, while the space complexity is O(n) for storing the words in a set.

What is the brute force solution for Longest Word in Dictionary?

The brute force approach for Longest Word in Dictionary is Brute Force, with O(n²) time complexity and O(1) space complexity. In this approach, we will check each word in the list to see if all of its prefixes exist in the list. This is a straightforward method but can be inefficient as it requires multiple checks for each word. The optimal Optimal Solution approach improves this to O(n log n).

What algorithm or data structure is used to solve Longest Word in Dictionary?

Longest Word in Dictionary uses the following concepts: Array, Hash Table, String, Trie, Sorting. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Longest Word in Dictionary?

Always consider edge cases, such as single-character words. Explain your thought process clearly while coding. Don't forget to test your solution with multiple inputs.

What are common mistakes when solving Longest Word in Dictionary?

Not checking all prefixes correctly. Forgetting to handle the lexicographical order when lengths are the same.

#720

Longest Word in Dictionary

Medium

ArrayHash TableStringTrieSortingHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

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Intuition

Time O(n log n)Space O(n)

This approach uses a set to store the words for quick lookup. By sorting the words first, we ensure that we can build longer words in lexicographical order efficiently.

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Algorithm

5 steps

1Step 1: Sort the words array lexicographically.
2Step 2: Initialize a set to store the words and a variable for the longest word.
3Step 3: Iterate through the sorted words and check if the current word can be formed by its prefixes in the set.
4Step 4: If valid, update the longest word.
5Step 5: Add the current word to the set.

solution.py9 lines

1def longestWord(words):
2    words.sort()
3    word_set = set()
4    longest = ''
5    for word in words:
6        if len(word) == 1 or word[:-1] in word_set:
7            longest = word if len(word) > len(longest) else longest
8            word_set.add(word)
9    return longest

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Complexity note: The time complexity is O(n log n) due to the sorting step, while the space complexity is O(n) for storing the words in a set.

1Sorting the words helps in checking prefixes in lexicographical order.
2Using a set allows for O(1) average time complexity for lookups.

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