Swift Implementation for LCCI 17.15

Author: klever34

lcci/17.15.Longest Word/README.md

@@ -199,6 +199,73 @@ func longestWord(words []string) string {
 }
 ```
 
+```swift
+class Trie {
+    var children = [Trie?](repeating: nil, count: 26)
+    var isEnd = false
+
+    func insert(_ word: String) {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                node.children[index] = Trie()
+            }
+            node = node.children[index]!
+        }
+        node.isEnd = true
+    }
+
+    func search(_ word: String) -> Bool {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                return false
+            }
+            node = node.children[index]!
+        }
+        return node.isEnd
+    }
+}
+
+class Solution {
+    private let trie = Trie()
+
+    func longestWord(_ words: [String]) -> String {
+        let sortedWords = words.sorted { a, b in
+            if a.count != b.count {
+                return a.count < b.count
+            }
+            return a > b
+        }
+
+        var ans = ""
+        for word in sortedWords {
+            if dfs(word, "") {
+                ans = word
+            }
+            trie.insert(word)
+        }
+        return ans
+    }
+
+    private func dfs(_ word: String, _ prefix: String) -> Bool {
+        if prefix.isEmpty {
+            return true
+        }
+        for i in 1...prefix.count {
+            let index = prefix.index(prefix.startIndex, offsetBy: i)
+            let subPrefix = String(prefix[..<index])
+            if trie.search(subPrefix) && dfs(word, String(prefix[index...])) {
+                return true
+            }
+        }
+        return false
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.15.Longest Word/README_EN.md

@@ -207,6 +207,73 @@ func longestWord(words []string) string {
 }
 ```
 
+```swift
+class Trie {
+    var children = [Trie?](repeating: nil, count: 26)
+    var isEnd = false
+
+    func insert(_ word: String) {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                node.children[index] = Trie()
+            }
+            node = node.children[index]!
+        }
+        node.isEnd = true
+    }
+
+    func search(_ word: String) -> Bool {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                return false
+            }
+            node = node.children[index]!
+        }
+        return node.isEnd
+    }
+}
+
+class Solution {
+    private let trie = Trie()
+
+    func longestWord(_ words: [String]) -> String {
+        let sortedWords = words.sorted { a, b in
+            if a.count != b.count {
+                return a.count < b.count
+            }
+            return a > b
+        }
+
+        var ans = ""
+        for word in sortedWords {
+            if dfs(word, "") {
+                ans = word
+            }
+            trie.insert(word)
+        }
+        return ans
+    }
+
+    private func dfs(_ word: String, _ prefix: String) -> Bool {
+        if prefix.isEmpty {
+            return true
+        }
+        for i in 1...prefix.count {
+            let index = prefix.index(prefix.startIndex, offsetBy: i)
+            let subPrefix = String(prefix[..<index])
+            if trie.search(subPrefix) && dfs(word, String(prefix[index...])) {
+                return true
+            }
+        }
+        return false
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.15.Longest Word/Solution.swift

@@ -0,0 +1,64 @@
+class Trie {
+    var children = [Trie?](repeating: nil, count: 26)
+    var isEnd = false
+
+    func insert(_ word: String) {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                node.children[index] = Trie()
+            }
+            node = node.children[index]!
+        }
+        node.isEnd = true
+    }
+
+    func search(_ word: String) -> Bool {
+        var node = self
+        for ch in word {
+            let index = Int(ch.asciiValue! - Character("a").asciiValue!)
+            if node.children[index] == nil {
+                return false
+            }
+            node = node.children[index]!
+        }
+        return node.isEnd
+    }
+}
+
+class Solution {
+    private let trie = Trie()
+
+    func longestWord(_ words: [String]) -> String {
+        let sortedWords = words.sorted { a, b in
+            if a.count != b.count {
+                return a.count < b.count
+            }
+            return a > b
+        }
+
+        var ans = ""
+        for word in sortedWords {
+            if dfs(word, "") {
+                ans = word
+            }
+            trie.insert(word)
+        }
+        return ans
+    }
+
+    private func dfs(_ word: String, _ prefix: String) -> Bool {
+        if prefix.isEmpty {
+            return true
+        }
+        for i in 1...prefix.count {
+            let index = prefix.index(prefix.startIndex, offsetBy: i)
+            let subPrefix = String(prefix[..<index])
+            if trie.search(subPrefix) && dfs(word, String(prefix[index...])) {
+                return true
+            }
+        }
+        return false
+    }
+}