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Prefix matching in Python using pytrie module

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  • Difficulty Level : Easy
  • Last Updated : 21 Jul, 2022
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Given a list of strings and a prefix value sub-string, find all strings from given list of strings which contains given value as prefix ? Examples:

Input : arr = ['geeksforgeeks', 'forgeeks', 
               'geeks', 'eeksfor'], 
       prefix = 'geek'
Output : ['geeksforgeeks','geeks']

A Simple approach to solve this problem is to traverse through complete list and match given prefix with each string one by one, print all strings which contains given value as prefix. We have existing solution to solve this problem using Trie Data Structure. We can implement Trie in python using pytrie.StringTrie() module.

Create, insert, search and delete in pytrie.StringTrie() ?

  • Create : trie=pytrie.StringTrie() creates a empty trie data structure.
  • Insert : trie[key]=value, key is the data we want to insert in trie and value is similar to bucket which gets appended just after the last node of inserted key and this bucket contains the actual value of key inserted.
  • Search : trie.values(prefix), returns list of all keys which contains given prefix.
  • Delete : del trie[key], removes specified key from trie data structure.

Note : To install pytrie package use this pip install pytrie –user command from terminal in linux


# Function which returns all strings
# that contains given prefix
from pytrie import StringTrie
def prefixSearch(arr,prefix):
    # create empty trie
    # traverse through list of strings
    # to insert it in trie. Here value of
    # key is itself key because at last
    # we need to return
    for key in arr:
        trie[key] = key
    # values(search) method returns list
    # of values of keys which contains
    # search pattern as prefix
    return trie.values(prefix)
# Driver program
if __name__ == "__main__":
    arr = ['geeksforgeeks','forgeeks','geeks','eeksfor']
    prefix = 'geek'
    output = prefixSearch(arr,prefix)
    if len(output) > 0:
        print (output)
        print ('Pattern not found')



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