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feat: update leetcode solutions: No.0208. Implement Trie (Prefix Tree)
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‎solution/0200-0299/0208.Implement Trie (Prefix Tree)/README.md

+131-2
Original file line numberDiff line numberDiff line change
@@ -29,22 +29,151 @@ trie.search(&quot;app&quot;); // 返回 true</pre>
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<!-- 这里可写通用的实现逻辑 -->
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前缀树每个节点包括两部分：
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1. 指向子节点的指针数组 children，对于本题而言，数组长度为 26，即小写英文字母的数量。`children[0]` 对应小写字母 a，...，`children[25]` 对应小写字母 z。
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1. 布尔字段 `isEnd`，表示该节点是否为字符串的结尾。
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### 1. 插入字符串
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我们从字典树的根开始，插入字符串。对于当前字符对应的子节点，有两种情况：
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- 子节点存在。沿着指针移动到子节点，继续处理下一个字符。
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- 子节点不存在。创建一个新的子节点，记录在 `children` 数组的对应位置上，然后沿着指针移动到子节点，继续搜索下一个字符。
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重复以上步骤，直到处理字符串的最后一个字符，然后将当前节点标记为字符串的结尾。
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### 2. 查找前缀
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我们从字典树的根开始，查找前缀。对于当前字符对应的子节点，有两种情况：
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- 子节点存在。沿着指针移动到子节点，继续搜索下一个字符。
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- 子节点不存在。说明字典树中不包含该前缀，返回空指针。
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重复以上步骤，直到返回空指针或搜索完前缀的最后一个字符。
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若搜索到了前缀的末尾，就说明字典树中存在该前缀。此外，若前缀末尾对应节点的 `isEnd` 为真，则说明字典树中存在该字符串。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Trie:
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def __init__(self):
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"""
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Initialize your data structure here.
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"""
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self.children = [None] * 26
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self.is_end = False
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def insert(self, word: str) -> None:
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"""
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Inserts a word into the trie.
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"""
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node = self
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for c in word:
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index = ord(c) - ord("a")
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if node.children[index] is None:
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node.children[index] = Trie()
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node = node.children[index]
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node.is_end = True
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def search(self, word: str) -> bool:
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"""
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Returns if the word is in the trie.
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"""
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node = self._search_prefix(word)
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return node is not None and node.is_end
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def startsWith(self, prefix: str) -> bool:
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"""
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Returns if there is any word in the trie that starts with the given prefix.
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"""
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node = self._search_prefix(prefix)
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return node is not None
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def _search_prefix(self, prefix: str):
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node = self
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for c in prefix:
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index = ord(c) - ord("a")
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if node.children[index] is None:
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return None
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node = node.children[index]
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return node
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# Your Trie object will be instantiated and called as such:
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# obj = Trie()
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# obj.insert(word)
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# param_2 = obj.search(word)
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# param_3 = obj.startsWith(prefix)
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Trie {
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private Trie[] children;
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private boolean isEnd;
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/** Initialize your data structure here. */
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public Trie() {
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children = new Trie[26];
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isEnd = false;
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}
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/** Inserts a word into the trie. */
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public void insert(String word) {
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Trie node = this;
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for (int i = 0; i < word.length(); ++i) {
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char c = word.charAt(i);
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int index = c - 'a';
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if (node.children[index] == null) {
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node.children[index] = new Trie();
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}
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node = node.children[index];
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}
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node.isEnd = true;
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}
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/** Returns if the word is in the trie. */
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public boolean search(String word) {
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Trie node = searchPrefix(word);
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return node != null && node.isEnd;
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}
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/** Returns if there is any word in the trie that starts with the given prefix. */
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public boolean startsWith(String prefix) {
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Trie node = searchPrefix(prefix);
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return node != null;
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}
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private Trie searchPrefix(String prefix) {
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Trie node = this;
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for (int i = 0; i < prefix.length(); ++i) {
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char c = prefix.charAt(i);
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int index = c - 'a';
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if (node.children[index] == null) {
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return null;
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}
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node = node.children[index];
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}
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return node;
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}
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}
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/**
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* Your Trie object will be instantiated and called as such:
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* Trie obj = new Trie();
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* obj.insert(word);
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* boolean param_2 = obj.search(word);
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* boolean param_3 = obj.startsWith(prefix);
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*/
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```
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### **...**

‎solution/0200-0299/0208.Implement Trie (Prefix Tree)/README_EN.md

+106-2
Original file line numberDiff line numberDiff line change
@@ -42,13 +42,117 @@ trie.search(&quot;app&quot;); // returns true
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### **Python3**
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```python
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class Trie:
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def __init__(self):
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"""
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Initialize your data structure here.
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"""
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self.children = [None] * 26
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self.is_end = False
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def insert(self, word: str) -> None:
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"""
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Inserts a word into the trie.
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"""
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node = self
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for c in word:
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index = ord(c) - ord("a")
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if node.children[index] is None:
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node.children[index] = Trie()
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node = node.children[index]
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node.is_end = True
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def search(self, word: str) -> bool:
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"""
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Returns if the word is in the trie.
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"""
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node = self._search_prefix(word)
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return node is not None and node.is_end
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def startsWith(self, prefix: str) -> bool:
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"""
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Returns if there is any word in the trie that starts with the given prefix.
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"""
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node = self._search_prefix(prefix)
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return node is not None
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def _search_prefix(self, prefix: str):
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node = self
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for c in prefix:
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index = ord(c) - ord("a")
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if node.children[index] is None:
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return None
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node = node.children[index]
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return node
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# Your Trie object will be instantiated and called as such:
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# obj = Trie()
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# obj.insert(word)
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# param_2 = obj.search(word)
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# param_3 = obj.startsWith(prefix)
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```
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### **Java**
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```java
51-
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class Trie {
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private Trie[] children;
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private boolean isEnd;
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/** Initialize your data structure here. */
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public Trie() {
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children = new Trie[26];
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isEnd = false;
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}
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/** Inserts a word into the trie. */
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public void insert(String word) {
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Trie node = this;
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for (int i = 0; i < word.length(); ++i) {
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char c = word.charAt(i);
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int index = c - 'a';
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if (node.children[index] == null) {
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node.children[index] = new Trie();
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}
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node = node.children[index];
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}
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node.isEnd = true;
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}
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/** Returns if the word is in the trie. */
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public boolean search(String word) {
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Trie node = searchPrefix(word);
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return node != null && node.isEnd;
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}
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/** Returns if there is any word in the trie that starts with the given prefix. */
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public boolean startsWith(String prefix) {
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Trie node = searchPrefix(prefix);
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return node != null;
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}
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private Trie searchPrefix(String prefix) {
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Trie node = this;
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for (int i = 0; i < prefix.length(); ++i) {
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char c = prefix.charAt(i);
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int index = c - 'a';
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if (node.children[index] == null) {
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return null;
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}
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node = node.children[index];
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}
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return node;
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}
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}
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/**
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* Your Trie object will be instantiated and called as such:
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* Trie obj = new Trie();
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* obj.insert(word);
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* boolean param_2 = obj.search(word);
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* boolean param_3 = obj.startsWith(prefix);
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*/
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```
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### **...**

‎solution/0200-0299/0208.Implement Trie (Prefix Tree)/Solution.java

+43-62
Original file line numberDiff line numberDiff line change
@@ -1,76 +1,57 @@
11
class Trie {
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private Trie[] children;
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private boolean isEnd;
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class TrieNode {
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private TrieNode[] links;
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private final int R = 26;
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private boolean isEnd;
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public TrieNode() {
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links = new TrieNode[R];
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}
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public boolean containsKey(char ch) {
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return links[ch -'a'] != null;
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}
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public TrieNode get(char ch) {
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return links[ch -'a'];
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}
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public void put(char ch, TrieNode node) {
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links[ch -'a'] = node;
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}
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public void setEnd() {
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isEnd = true;
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}
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public boolean isEnd() {
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return isEnd;
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}
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}
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private TrieNode root;
37-
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/** Initialize your data structure here. */
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public Trie() {
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root = new TrieNode();
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children = new Trie[26];
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isEnd = false;
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}
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/** Inserts a word into the trie. */
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public void insert(String word) {
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TrieNode node = root;
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for (int i = 0; i < word.length(); i++) {
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char currentChar = word.charAt(i);
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if (!node.containsKey(currentChar)) {
47-
node.put(currentChar, new TrieNode());
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Trie node = this;
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for (int i = 0; i < word.length(); ++i) {
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char c = word.charAt(i);
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int index = c - 'a';
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if (node.children[index] == null) {
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node.children[index] = new Trie();
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}
49-
node = node.get(currentChar);
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node = node.children[index];
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}
51-
node.setEnd();
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node.isEnd = true;
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}
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/** Returns if the word is in the trie. */
26+
public boolean search(String word) {
27+
Trie node = searchPrefix(word);
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return node != null && node.isEnd;
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}
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/** Returns if there is any word in the trie that starts with the given prefix. */
32+
public boolean startsWith(String prefix) {
33+
Trie node = searchPrefix(prefix);
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return node != null;
5235
}
5336

54-
private TrieNode searchPrefix(String word) {
55-
TrieNode node = root;
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for (int i = 0; i < word.length(); i++) {
57-
char curLetter = word.charAt(i);
58-
if (node.containsKey(curLetter)) {
59-
node = node.get(curLetter);
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} else {
37+
private Trie searchPrefix(String prefix) {
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Trie node = this;
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for (int i = 0; i < prefix.length(); ++i) {
40+
char c = prefix.charAt(i);
41+
int index = c - 'a';
42+
if (node.children[index] == null) {
6143
return null;
6244
}
45+
node = node.children[index];
6346
}
6447
return node;
6548
}
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67-
public boolean search(String word) {
68-
TrieNode node = searchPrefix(word);
69-
return node != null && node.isEnd();
70-
}
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public boolean startsWith(String prefix) {
73-
TrieNode node = searchPrefix(prefix);
74-
return node != null;
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}
76-
}
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}
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/**
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* Your Trie object will be instantiated and called as such:
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* Trie obj = new Trie();
54+
* obj.insert(word);
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* boolean param_2 = obj.search(word);
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* boolean param_3 = obj.startsWith(prefix);
57+
*/

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