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feat: add solutions to leetcode problem: No.1804. Implement Trie II (Prefix Tree)
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‎README.md

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@@ -173,6 +173,7 @@
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### 设计
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- [实现 Trie (前缀树)](/solution/0200-0299/0208.Implement%20Trie%20%28Prefix%20Tree%29/README.md)
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- [实现 Trie （前缀树） II](/solution/1800-1899/1804.Implement%20Trie%20II%20%28Prefix%20Tree%29/README.md)
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- [设计哈希集合](/solution/0700-0799/0705.Design%20HashSet/README.md)
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- [设计哈希映射](/solution/0700-0799/0706.Design%20HashMap/README.md)
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‎README_EN.md

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@@ -166,6 +166,7 @@ Complete solutions to [LeetCode](https://leetcode-cn.com/problemset/all/), [LCOF
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### Design
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- [Implement Trie (Prefix Tree)](<solution/0200-0299/0208.Implement%20Trie%20(Prefix%20Tree)/README_EN.md>)
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- [Implement Trie II (Prefix Tree)](/solution/1800-1899/1804.Implement%20Trie%20II%20%28Prefix%20Tree%29/README_EN.md)
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- [Design HashSet](/solution/0700-0799/0705.Design%20HashSet/README_EN.md)
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- [Design HashMap](/solution/0700-0799/0706.Design%20HashMap/README_EN.md)
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‎images/contributors.svg

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‎solution/1800-1899/1804.Implement Trie II (Prefix Tree)/README.md

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@@ -52,27 +52,161 @@ trie.countWordsStartingWith("app"); // 返回 0
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<li>保证每次调用 <code>erase</code> 时，字符串 <code>word</code> 总是存在于前缀树中。</li>
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</ul>
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## 解法
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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三部分：
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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. int 变量 `count`，表示以该节点结尾的字符串个数。
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1. int 变量 `preCount`，表示以该节点作为前缀节点的字符串个数。
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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，让子节点的 `preCount` 值加 1。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，然后将当前节点的 `count` 值加 1。
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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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<!-- 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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self.children = [None] * 26
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self.count = 0
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self.pre_count = 0
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def insert(self, word: str) -> None:
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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.pre_count += 1
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node.count += 1
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def countWordsEqualTo(self, word: str) -> int:
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node = self._search_prefix(word)
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return 0 if node is None else node.count
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def countWordsStartingWith(self, prefix: str) -> int:
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node = self._search_prefix(prefix)
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return 0 if node is None else node.pre_count
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def erase(self, word: str) -> None:
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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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node = node.children[index]
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node.pre_count -= 1
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node.count -= 1
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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.countWordsEqualTo(word)
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# param_3 = obj.countWordsStartingWith(prefix)
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# obj.erase(word)
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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 int count;
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private int preCount;
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public Trie() {
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children = new Trie[26];
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count = 0;
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preCount = 0;
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}
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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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int index = word.charAt(i) - '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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node.preCount += 1;
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}
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node.count += 1;
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}
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public int countWordsEqualTo(String word) {
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Trie node = searchPrefix(word);
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return node == null ? 0 : node.count;
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}
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public int countWordsStartingWith(String prefix) {
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Trie node = searchPrefix(prefix);
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return node == null ? 0 : node.preCount;
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}
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public void erase(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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int index = word.charAt(i) - 'a';
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node = node.children[index];
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node.preCount -= 1;
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}
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node.count -= 1;
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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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int index = prefix.charAt(i) - '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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* int param_2 = obj.countWordsEqualTo(word);
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* int param_3 = obj.countWordsStartingWith(prefix);
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* obj.erase(word);
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*/
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```
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### **...**

‎solution/1800-1899/1804.Implement Trie II (Prefix Tree)/README_EN.md

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@@ -49,21 +49,131 @@ trie.countWordsStartingWith(&quot;app&quot;); // return 0
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<li>It is guaranteed that for any function call to <code>erase</code>, the string <code>word</code> will exist in the trie.</li>
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</ul>
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## Solutions
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<!-- tabs:start -->
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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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self.children = [None] * 26
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self.count = 0
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self.pre_count = 0
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def insert(self, word: str) -> None:
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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.pre_count += 1
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node.count += 1
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def countWordsEqualTo(self, word: str) -> int:
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node = self._search_prefix(word)
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return 0 if node is None else node.count
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def countWordsStartingWith(self, prefix: str) -> int:
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node = self._search_prefix(prefix)
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return 0 if node is None else node.pre_count
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def erase(self, word: str) -> None:
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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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node = node.children[index]
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node.pre_count -= 1
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node.count -= 1
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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.countWordsEqualTo(word)
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# param_3 = obj.countWordsStartingWith(prefix)
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# obj.erase(word)
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```
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### **Java**
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```java
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class Trie {
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private Trie[] children;
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private int count;
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private int preCount;
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public Trie() {
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children = new Trie[26];
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count = 0;
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preCount = 0;
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}
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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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int index = word.charAt(i) - '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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node.preCount += 1;
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}
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node.count += 1;
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}
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public int countWordsEqualTo(String word) {
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Trie node = searchPrefix(word);
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return node == null ? 0 : node.count;
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}
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public int countWordsStartingWith(String prefix) {
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Trie node = searchPrefix(prefix);
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return node == null ? 0 : node.preCount;
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}
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public void erase(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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int index = word.charAt(i) - 'a';
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node = node.children[index];
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node.preCount -= 1;
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}
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node.count -= 1;
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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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int index = prefix.charAt(i) - '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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* int param_2 = obj.countWordsEqualTo(word);
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* int param_3 = obj.countWordsStartingWith(prefix);
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* obj.erase(word);
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*/
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```
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### **...**

‎solution/1800-1899/1804.Implement Trie II (Prefix Tree)/Solution.java

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class Trie {
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private Trie[] children;
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private int count;
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private int preCount;
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public Trie() {
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children = new Trie[26];
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count = 0;
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preCount = 0;
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}
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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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int index = word.charAt(i) - '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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node.preCount += 1;
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}
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node.count += 1;
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}
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public int countWordsEqualTo(String word) {
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Trie node = searchPrefix(word);
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return node == null ? 0 : node.count;
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}
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public int countWordsStartingWith(String prefix) {
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Trie node = searchPrefix(prefix);
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return node == null ? 0 : node.preCount;
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}
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public void erase(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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int index = word.charAt(i) - 'a';
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node = node.children[index];
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node.preCount -= 1;
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}
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node.count -= 1;
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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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int index = prefix.charAt(i) - '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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* int param_2 = obj.countWordsEqualTo(word);
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* int param_3 = obj.countWordsStartingWith(prefix);
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* obj.erase(word);
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*/

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