feat: Add solution for LeetCode problem 211

Author: WhiteHyun

design-add-and-search-words-data-structure/WhiteHyun.swift

@@ -0,0 +1,55 @@
+//
+//  211. Design Add and Search Words Data Structure
+//  https://leetcode.com/problems/design-add-and-search-words-data-structure/description/
+//  Dale-Study
+//
+//  Created by WhiteHyun on 2024/06/28.
+//
+
+private final class Node {
+  var children: [Character: Node]
+  var endOfWord: Bool
+
+  init(
+    children: [Character: Node] = [:],
+    endOfWord: Bool = false
+  ) {
+    self.children = children
+    self.endOfWord = endOfWord
+  }
+}
+
+final class WordDictionary {
+  private let root: Node
+
+  init() {
+    root = Node()
+  }
+
+  func addWord(_ word: String) {
+    var node = root
+    for character in word {
+      if node.children[character] == nil {
+        node.children[character] = Node()
+      }
+      node = node.children[character]!
+    }
+    node.endOfWord = true
+  }
+
+  func search(_ word: String) -> Bool {
+    let word = Array(word)
+    func dfs(index: Int, node: Node) -> Bool {
+      guard index < word.count else { return node.endOfWord }
+
+      let character = word[index]
+      if character == "." {
+        return node.children.values.contains { dfs(index: index + 1, node: $0) }
+      } else if let nextNode = node.children[character] {
+        return dfs(index: index + 1, node: nextNode)
+      }
+      return false
+    }
+    return dfs(index: 0, node: root)
+  }
+}