[LeetCode] 208. Implement Trie (Prefix Tree)_Medium tag: Trie
阿新 • • 發佈:2021-06-29
Atrie(pronounced as "try") orprefix treeis a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.
Implement the Trie class:
Trie()
Initializes the trie object.void insert(String word)
word
into the trie.boolean search(String word)
Returnstrue
if the stringword
is in the trie (i.e., was inserted before), andfalse
otherwise.boolean startsWith(String prefix)
Returnstrue
if there is a previously inserted stringword
that has the prefixprefix
, andfalse
otherwise.
Example 1:
Input ["Trie", "insert", "search", "search", "startsWith", "insert", "search"] [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]] Output [null, null, true, false, true, null, true] Explanation Trie trie = new Trie(); trie.insert("apple"); trie.search("apple"); // return True trie.search("app"); // return False trie.startsWith("app"); // return True trie.insert("app"); trie.search("app"); // return True
Constraints:
1 <= word.length, prefix.length <= 2000
word
andprefix
consist only of lowercase English letters.- At most
3 * 104
callsin totalwill be made toinsert
,search
, andstartsWith
.
Ideas, 建立一個TrieNode 的class, 有兩個property, bool: isWord 來判斷是否是一個word, dict : children 來存 c -> TrieNode.
class TrieNode: def __init__(self): self.isWord = False self.children = dict() class Trie: def __init__(self): """ Initialize your data structure here. """ self.root = TrieNode() def insert(self, word: str) -> None: """ Inserts a word into the trie. """ node = self.root for c in word: if c not in node.children: node.children[c] = TrieNode() node = node.children[c] node.isWord = True def search(self, word: str) -> bool: """ Returns if the word is in the trie. """ node = self.root for c in word: if c not in node.children: return False node = node.children[c] return node.isWord def startsWith(self, prefix: str) -> bool: """ Returns if there is any word in the trie that starts with the given prefix. """ node = self.root for c in prefix: if c not in node.children: return False node= node.children[c] return True # Your Trie object will be instantiated and called as such: # obj = Trie() # obj.insert(word) # param_2 = obj.search(word) # param_3 = obj.startsWith(prefix)