Leetcode 75

Solution/208. Implement Trie (Prefix Tree)/208. Implement Trie (Prefix Tree).py

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+class Trie:
+    def __init__(self):
+        self.children = [None] * 26
+        self.is_end = False
+
+    def insert(self, word: str) -> None:
+        node = self
+        for c in word:
+            idx = ord(c) - ord('a')
+            if node.children[idx] is None:
+                node.children[idx] = Trie()
+            node = node.children[idx]
+        node.is_end = True
+
+    def search(self, word: str) -> bool:
+        node = self._search_prefix(word)
+        return node is not None and node.is_end
+
+    def startsWith(self, prefix: str) -> bool:
+        node = self._search_prefix(prefix)
+        return node is not None
+
+    def _search_prefix(self, prefix: str):
+        node = self
+        for c in prefix:
+            idx = ord(c) - ord('a')
+            if node.children[idx] is None:
+                return None
+            node = node.children[idx]
+        return node
+
+
+# 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)

Solution/208. Implement Trie (Prefix Tree)/readme.md

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+---
+comments: true
+difficulty: Medium
+edit_url: Antim
+tags:
+    - Design
+    - Trie
+    - Hash Table
+    - String
+---
+
+<!-- problem:start -->
+
+# [208. Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree)
+
+
+## Description
+
+<!-- description:start -->
+
+<p>A <a href="https://en.wikipedia.org/wiki/Trie" target="_blank"><strong>trie</strong></a> (pronounced as &quot;try&quot;) or <strong>prefix tree</strong> is 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.</p>
+
+<p>Implement the Trie class:</p>
+
+<ul>
+	<li><code>Trie()</code> Initializes the trie object.</li>
+	<li><code>void insert(String word)</code> Inserts the string <code>word</code> into the trie.</li>
+	<li><code>boolean search(String word)</code> Returns <code>true</code> if the string <code>word</code> is in the trie (i.e., was inserted before), and <code>false</code> otherwise.</li>
+	<li><code>boolean startsWith(String prefix)</code> Returns <code>true</code> if there is a previously inserted string <code>word</code> that has the prefix <code>prefix</code>, and <code>false</code> otherwise.</li>
+</ul>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input</strong>
+[&quot;Trie&quot;, &quot;insert&quot;, &quot;search&quot;, &quot;search&quot;, &quot;startsWith&quot;, &quot;insert&quot;, &quot;search&quot;]
+[[], [&quot;apple&quot;], [&quot;apple&quot;], [&quot;app&quot;], [&quot;app&quot;], [&quot;app&quot;], [&quot;app&quot;]]
+<strong>Output</strong>
+[null, null, true, false, true, null, true]
+
+<strong>Explanation</strong>
+Trie trie = new Trie();
+trie.insert(&quot;apple&quot;);
+trie.search(&quot;apple&quot;);   // return True
+trie.search(&quot;app&quot;);     // return False
+trie.startsWith(&quot;app&quot;); // return True
+trie.insert(&quot;app&quot;);
+trie.search(&quot;app&quot;);     // return True
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= word.length, prefix.length &lt;= 2000</code></li>
+	<li><code>word</code> and <code>prefix</code> consist only of lowercase English letters.</li>
+	<li>At most <code>3 * 10<sup>4</sup></code> calls <strong>in total</strong> will be made to <code>insert</code>, <code>search</code>, and <code>startsWith</code>.</li>
+</ul>
+
+<!-- description:end -->
+
+## Solutions
+
+<!-- solution:start -->
+
+### Solution 1
+
+<!-- tabs:start -->
+
+#### Python3
+
+```python
+class Trie:
+    def __init__(self):
+        self.children = [None] * 26
+        self.is_end = False
+
+    def insert(self, word: str) -> None:
+        node = self
+        for c in word:
+            idx = ord(c) - ord('a')
+            if node.children[idx] is None:
+                node.children[idx] = Trie()
+            node = node.children[idx]
+        node.is_end = True
+
+    def search(self, word: str) -> bool:
+        node = self._search_prefix(word)
+        return node is not None and node.is_end
+
+    def startsWith(self, prefix: str) -> bool:
+        node = self._search_prefix(prefix)
+        return node is not None
+
+    def _search_prefix(self, prefix: str):
+        node = self
+        for c in prefix:
+            idx = ord(c) - ord('a')
+            if node.children[idx] is None:
+                return None
+            node = node.children[idx]
+        return node
+
+
+# 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)
+```
+
+#### Java
+
+```java
+class Trie {
+    private Trie[] children;
+    private boolean isEnd;
+
+    public Trie() {
+        children = new Trie[26];
+    }
+
+    public void insert(String word) {
+        Trie node = this;
+        for (char c : word.toCharArray()) {
+            int idx = c - 'a';
+            if (node.children[idx] == null) {
+                node.children[idx] = new Trie();
+            }
+            node = node.children[idx];
+        }
+        node.isEnd = true;
+    }
+
+    public boolean search(String word) {
+        Trie node = searchPrefix(word);
+        return node != null && node.isEnd;
+    }
+
+    public boolean startsWith(String prefix) {
+        Trie node = searchPrefix(prefix);
+        return node != null;
+    }
+
+    private Trie searchPrefix(String s) {
+        Trie node = this;
+        for (char c : s.toCharArray()) {
+            int idx = c - 'a';
+            if (node.children[idx] == null) {
+                return null;
+            }
+            node = node.children[idx];
+        }
+        return node;
+    }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie obj = new Trie();
+ * obj.insert(word);
+ * boolean param_2 = obj.search(word);
+ * boolean param_3 = obj.startsWith(prefix);
+ */
+```
+
+#### C++
+
+```cpp
+class Trie {
+private:
+    vector<Trie*> children;
+    bool isEnd;
+
+    Trie* searchPrefix(string s) {
+        Trie* node = this;
+        for (char c : s) {
+            int idx = c - 'a';
+            if (!node->children[idx]) return nullptr;
+            node = node->children[idx];
+        }
+        return node;
+    }
+
+public:
+    Trie()
+        : children(26)
+        , isEnd(false) {}
+
+    void insert(string word) {
+        Trie* node = this;
+        for (char c : word) {
+            int idx = c - 'a';
+            if (!node->children[idx]) node->children[idx] = new Trie();
+            node = node->children[idx];
+        }
+        node->isEnd = true;
+    }
+
+    bool search(string word) {
+        Trie* node = searchPrefix(word);
+        return node != nullptr && node->isEnd;
+    }
+
+    bool startsWith(string prefix) {
+        Trie* node = searchPrefix(prefix);
+        return node != nullptr;
+    }
+};
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie* obj = new Trie();
+ * obj->insert(word);
+ * bool param_2 = obj->search(word);
+ * bool param_3 = obj->startsWith(prefix);
+ */
+```
+
+<!-- tabs:end -->
+
+<!-- solution:end -->
+
+<!-- problem:end -->