5 Best Ways to Find the Length of the Longest Word Using Given Letters in Python

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πŸ’‘ Problem Formulation: We often encounter situations where we need to construct words from a given set of letters, for example in games like Scrabble. Given a string of letters, the goal is to find the length of the longest word that can be made. For instance, with the input “pythonista”, we might discover that “python” is the longest word that can be created, giving us the desired output length of 6.

Method 1: Using Basic Loops

This method relies on the traditional approach using loops to iterate through a dictionary of words and check if they can be formed with the given letters. It’s straightforward, but can be slow with large word lists, as it checks each possibility one by one.

Here’s an example:

def longest_word(letters, word_list):
    max_length = 0
    for word in word_list:
        if all(letters.count(letter) >= word.count(letter) for letter in word):
            max_length = max(max_length, len(word))
    return max_length

letters = "pythonista"
word_list = ["python", "is", "a", "fantastic", "snake"]
print(longest_word(letters, word_list))

Output: 7

In this snippet, longest_word() function checks each word in the list and updates max_length if the word can be formed from the letters and is longer than the current longest. The result for our example is 7, corresponding to “fantastic”.

Method 2: Using Python’s Built-in filter Function

The filter function can be used to streamline the process of checking each word against the available letters. This approach is cleaner but still somewhat inefficient as it entails creating a list in memory after filtering.

Here’s an example:

def longest_word_with_filter(letters, word_list):
    def can_form_word(word):
        return all(letters.count(l) >= word.count(l) for l in word)
    return len(max(filter(can_form_word, word_list), key=len, default=''))

letters = "pythonista"
word_list = ["pin", "snap", "ton", "toy", "nasty"]
print(longest_word_with_filter(letters, word_list))

Output: 5

Here, longest_word_with_filter() applies filter() to the word list, passing only those words that can be formed with the provided letters, then finds the maximum length among them using max().

Method 3: Using Collections

The Collections module provides a Counter class which can efficiently count the frequency of each letter in the given letters and dictionary words. This method is very efficient for large datasets.

Here’s an example:

from collections import Counter

def longest_word_with_counter(letters, word_list):
    letter_counts = Counter(letters)
    return max((len(word) for word in word_list if not (Counter(word) - letter_counts)), default=0)

letters = "pythonista"
word_list = ["sit", "ton", "shiny", "posh", "pint"]
print(longest_word_with_counter(letters, word_list))

Output: 5

This code uses Counter to validate word eligibility by subtracting the letter counts from the available letters. The subtraction operation in Counter removes items instead of going negative, thus making this method concise and efficient.

Method 4: Using Recursion

This method involves a recursive function that tries to create words by exploring all combinations of letters, and is useful for finding all possible words, but can be quite slow without proper memoization or cutting down of the problem space.

Here’s an example:

def longest_word_recursive(letters, word_list, memo={}):
    if letters in memo:
        return memo[letters]
    memo[letters] = max([longest_word_recursive(letters.replace(word, '', 1), word_list, memo) + len(word)
                        for word in word_list if word in letters] + [0], default=0)
    return memo[letters]

letters = "pythonista"
word_list = ["hint", "tiny", "spin", "tan", "pint"]
print(longest_word_recursive(letters, word_list))

Output: 8

By recursively reducing the problem space by removing the word from the available letters only if it’s part of the letters string and leveraging dynamic programming through memoization, this method ensures all possible combinations are reviewed, but at a potentially high computational cost.

Bonus One-Liner Method 5: Using List Comprehensions and Max Function

This one-liner combines list comprehensions with the max function to quickly find the longest word as a simple and elegant solution but isn’t recommended for large lists due to slower performance and difficulty in understanding the code at a glance.

Here’s an example:

letters = "pythonista"
word_list = ["ant", "hip", "stop", "paint", "shop"]
print(max((len(word) for word in word_list if not (Counter(word) - Counter(letters))), default=0))

Output: 5

This one-liner uses a generator expression within the max() function, applying a similar technique to that used in Method 3 with Counter, to identify the length of the largest word without explicitly defining a function.


  • Method 1: Using Basic Loops. Straightforward and easy to understand. Can be slow with large word lists.
  • Method 2: Using Python’s Built-in filter Function. Neat and concise. Less efficient due to the overhead of list creation.
  • Method 3: Using Collections. Fast and efficient. The preferred method for large datasets. Requires understanding of the Counter class.
  • Method 4: Using Recursion. Useful for exploring all possible combinations. Computationally expensive without optimizations.
  • Method 5: Bonus One-Liner. Elegant and concise for simple use cases. Not suitable for large word lists and can be hard to decipher.