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trie.py
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trie.py
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from typing import Tuple
class TrieNode(object):
"""
Our trie node implementation. Very basic. but does the job
"""
def __init__(self, char: str):
self.char = char
self.children = []
# Is it the last character of the word.`
self.word_finished = False
# How many times this character appeared in the addition process
self.counter = 1
def add(root, word: str):
"""
Adding a word in the trie structure
"""
node = root
for char in word:
found_in_child = False
# Search for the character in the children of the present `node`
for child in node.children:
if child.char == char:
# We found it, increase the counter by 1 to keep track that another
# word has it as well
child.counter += 1
# And point the node to the child that contains this char
node = child
found_in_child = True
break
# We did not find it so add a new chlid
if not found_in_child:
new_node = TrieNode(char)
node.children.append(new_node)
# And then point node to the new child
node = new_node
# Everything finished. Mark it as the end of a word.
node.word_finished = True
def find_prefix(root, prefix: str) -> Tuple[bool, int]:
"""
Check and return
1. If the prefix exsists in any of the words we added so far
2. If yes then how may words actually have the prefix
"""
node = root
# If the root node has no children, then return False.
# Because it means we are trying to search in an empty trie
if not root.children:
return False, 0
for char in prefix:
char_not_found = True
# Search through all the children of the present `node`
for child in node.children:
if child.char == char:
# We found the char existing in the child.
char_not_found = False
# Assign node as the child containing the char and break
node = child
break
# Return False anyway when we did not find a char.
if char_not_found:
return False, 0
# Well, we are here means we have found the prefix. Return true to indicate that
# And also the counter of the last node. This indicates how many words have this
# prefix
return True, node.counter
if __name__ == "__main__":
root = TrieNode('*')
add(root, "hackathon")
add(root, 'hack')
print(find_prefix(root, 'hac'))
print(find_prefix(root, 'hack'))
print(find_prefix(root, 'hackathon'))
print(find_prefix(root, 'ha'))
print(find_prefix(root, 'hammer'))