Question

Given a set of strings (large set), and an input string, you need to find all the anagrams of the input string efficiently. What data structure will you use. And using that, how will you find the anagrams?

Things that I have thought of are these:

1. Using maps

   a) eliminate all words with more/less letters than the input.

   b) put the input characters in map

   c) Traverse the map for each string and see if all letters are present with their count.

2. Using Tries

   a) Put all strings which have the right number of characters into a trie.

   b) traverse each branch and go deeper if the letter is contained in the input.

   c) if leaf reached the word is an anagram

Can anyone find a better solution?

Are there any problems that you find in the above approaches?

Answer 1

Build a frequency-map from each word and compare these maps.

Pseudo code:

class Word

  string word
  map<char, int> frequency

  Word(string w)
    word = w
    for char in word
      int count = frequency.get(char)
      if count == null
        count = 0
      count++
      frequency.put(char, count)

  boolean is_anagram_of(that)
    return this.frequency == that.frequency