feat: Add solution for LeetCode problem 208

Author: WhiteHyun

implement-trie-prefix-tree/WhiteHyun.swift

@@ -0,0 +1,64 @@
+//  
+//  208. Implement Trie (Prefix Tree)
+//  https://leetcode.com/problems/implement-trie-prefix-tree/description/
+//  Dale-Study
+//  
+//  Created by WhiteHyun on 2024/06/28.
+//  
+
+// MARK: - Node
+
+private class Node {
+  var children: [Character: Node]
+  let value: Character
+  var isEndOfWord: Bool
+
+  init(children: [Character: Node] = [:], value: Character, isEndOfWord: Bool = false) {
+    self.children = children
+    self.value = value
+    self.isEndOfWord = isEndOfWord
+  }
+}
+
+// MARK: - Trie
+
+class Trie {
+  private var root: Node
+
+  init() {
+    root = .init(value: "$")
+  }
+
+  func insert(_ word: String) {
+    var node = root
+    for character in word {
+      if node.children[character] == nil {
+        node.children[character] = Node(value: character)
+      }
+      node = node.children[character]!
+    }
+    node.isEndOfWord = true
+  }
+
+  func search(_ word: String) -> Bool {
+    var node = root
+    for character in word {
+      if node.children[character] == nil {
+        return false
+      }
+      node = node.children[character]!
+    }
+    return node.isEndOfWord
+  }
+
+  func startsWith(_ prefix: String) -> Bool {
+    var node = root
+    for character in prefix {
+      if node.children[character] == nil {
+        return false
+      }
+      node = node.children[character]!
+    }
+    return true
+  }
+}