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Implement Trie (Prefix Tree) in Python
Suppose we have to make the trie structure, with three basic operations like insert(), search(), startsWith() methods. We can assume that all inputs are in lowercase letters. For example, if we call the functions as follows, we will see the outputs
- Trie trie = new Trie()
- trie.insert(“apple”)
- trie.search(“apple”) //This will return true
- trie.search(“app”) //This will return false
- trie.startsWith(“app”) //This will return true
- trie.insert(“app”)
- trie.search(“app”) //This will return true
To solve this, we will follow these steps −
- Initially make one dictionary called child.
- The insert method will be like −
- current := child
- for each letter l in word −
- if l is not present in current, then current[l] := new dictionary
- current := current[l]
- current[#] = 1
- The search method will be like −
- current := child
- for each letter l in word −
- if l is not present in current, then return false
- current := current[l]
- return true if current[#] = 1, otherwise false
- The startsWith method will be like −
- current := child
- for each letter l in word −
- if l is not present in current, then return false
- current := current[l]
- return True
Let us see the following implementation to get better understanding −
Example
class Trie(object):
def __init__(self):
self.child = {}
def insert(self, word):
current = self.child
for l in word:
if l not in current:
current[l] = {}
current = current[l]
current['#']=1
def search(self, word):
current = self.child
for l in word:
if l not in current:
return False
current = current[l]
return '#' in current
def startsWith(self, prefix):
current = self.child
for l in prefix:
if l not in current:
return False
current = current[l]
return True
ob1 = Trie()
ob1.insert("apple")
print(ob1.search("apple"))
print(ob1.search("app"))
print(ob1.startsWith("app"))
ob1.insert("app")
print(ob1.search("app"))Input
ob1 = Trie()
ob1.insert("apple")
print(ob1.search("apple"))
print(ob1.search("app"))
print(ob1.startsWith("app"))
ob1.insert("app")
print(ob1.search("app"))Output
True False True True
Updated on: 04-May-2020
4K+ Views
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