LeetCode Trie Prefix Tree

Author: pertrai1

README.md

@@ -6,7 +6,7 @@ A comprehensive collection of coding challenges from multiple platforms for lear
 
 | Platform                         | Focus Area                   | Problems Solved |
 | -------------------------------- | ---------------------------- | --------------- |
-| [LeetCode](#-leetcode)           | Data Structures & Algorithms | 161             |
+| [LeetCode](#-leetcode)           | Data Structures & Algorithms | 162             |
 | [GreatFrontEnd](#-greatfrontend) | Frontend Engineering         | 5               |
 
 ## 🎯 Platforms
@@ -18,7 +18,7 @@ A comprehensive collection of coding challenges from multiple platforms for lear
 **Progress**:
 
 - Easy: 80 problems
-- Medium: 69 problems
+- Medium: 70 problems
 - Hard: 12 problems
 
 **Quick Links**:
@@ -180,11 +180,12 @@ A comprehensive collection of coding challenges from multiple platforms for lear
 </details>
 
 <details>
-<summary>🟡 Medium Problems (69 solved)</summary>
+<summary>🟡 Medium Problems (70 solved)</summary>
 
 ### Stack & Design
 
 - [0155 - Min Stack](./leetcode/medium/0155-min-stack) ![Medium](https://img.shields.io/badge/Medium-orange)
+- [0208 - Implement Trie (Prefix Tree)](./leetcode/medium/0208-implement-trie-prefix-tree) ![Medium](https://img.shields.io/badge/Medium-orange)
 
 ### Array & Two Pointers
 

leetcode/medium/0208-implement-trie-prefix-tree/README.md

@@ -0,0 +1,36 @@
+# [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree) ![Medium](https://img.shields.io/badge/Medium-orange)
+
+A [**trie**](https://en.wikipedia.org/wiki/Trie) (pronounced as "try") or **prefix tree** 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.
+
+Implement the Trie class:
+
+- `Trie()` Initializes the trie object.
+- `void insert(String word)` Inserts the string `word` into the trie.
+- `boolean search(String word)` Returns `true` if the string `word` is in the trie (i.e., was inserted before), and `false` otherwise.
+- `boolean startsWith(String prefix)` Returns `true` if there is a previously inserted string `word` that has the prefix `prefix`, and `false` otherwise.
+
+## Example 1
+
+```bash
+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` and `prefix` consist only of lowercase English letters.
+- At most `3 * 10^4` calls **in total** will be made to `insert`, `search`, and `startsWith`.

leetcode/medium/0208-implement-trie-prefix-tree/implement-trie-prefix-tree.ts

@@ -0,0 +1,76 @@
+class TrieNode {
+  children: { [key: string]: TrieNode } = {};
+  isEndOfWord: boolean = false;
+}
+
+/*
+ * @time - All operations run in O(L) time where L is the word length. This is because we process each character once.
+ * @space - Depends on the total number of characters across all words inserted, but shared prefixes help to reduce redundancy.
+ */
+class Trie {
+  private root: TrieNode;
+
+  constructor() {
+    this.root = new TrieNode();
+  }
+
+  // @time - O(L) where L is the length of the word
+  insert(word: string): void {
+    // Start at root
+    let current = this.root;
+    // For each char in word...
+    for (const char of word) {
+      // If char not in current.children, add new TrieNode
+      // Each lookup/insertion is O(1)
+      if (!current.children[char]) {
+        current.children[char] = new TrieNode();
+      }
+      // Move to the child node for this character
+      current = current.children[char];
+    }
+    // Mark the last node as end of a word
+    current.isEndOfWord = true;
+  }
+
+  // @time - O(L) where L is the length of the word
+  search(word: string): boolean {
+    let current = this.root;
+    // Traverse word
+    for (const char of word) {
+      // If char not found in current.children then the word does not exists
+      // Each child being accessed is O(1)
+      if (!current.children[char]) {
+        return false;
+      }
+      // Move to the child node
+      current = current.children[char];
+    }
+    // After traversing, check if current is end of the word
+    return current.isEndOfWord;
+  }
+
+  // @time - O(L) where L is the length of the prefix
+  startsWith(prefix: string): boolean {
+    // Same as search, but return true if path exists (ignore isEndOfWord)
+    let current = this.root;
+
+    for (const char of prefix) {
+      // Each child being accessed is O(1)
+      if (!current.children[char]) {
+        return false;
+      }
+      current = current.children[char];
+    }
+
+    // Full prefix path exits
+    return true;
+  }
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * var obj = new Trie()
+ * obj.insert(word)
+ * var param_2 = obj.search(word)
+ * var param_3 = obj.startsWith(prefix)
+ */