feat: add swift implementation to lcci problem: No.17.15 (doocs#2786)

---------

Co-authored-by: Libin YANG <contact@yanglibin.info>

Author: klever34

lcci/17.15.Longest Word/README.md

@@ -199,6 +199,66 @@ 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 {
+    func longestWord(_ words: [String]) -> String {
+        var words = words.sorted(by: { $0.count < $1.count || ($0.count == $1.count && $0 > $1) })
+        let trie = Trie()
+
+        var dfs: ((String) -> Bool)!
+        dfs = { w in
+            if w.isEmpty {
+                return true
+            }
+            for i in 1...w.count {
+                if trie.search(String(w.prefix(i))) && dfs(String(w.suffix(w.count - i))) {
+                    return true
+                }
+            }
+            return false
+        }
+
+        var ans = ""
+        for w in words {
+            if dfs(w) {
+                ans = w
+            }
+            trie.insert(w)
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.15.Longest Word/README_EN.md

@@ -207,6 +207,66 @@ 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 {
+    func longestWord(_ words: [String]) -> String {
+        var words = words.sorted(by: { $0.count < $1.count || ($0.count == $1.count && $0 > $1) })
+        let trie = Trie()
+
+        var dfs: ((String) -> Bool)!
+        dfs = { w in
+            if w.isEmpty {
+                return true
+            }
+            for i in 1...w.count {
+                if trie.search(String(w.prefix(i))) && dfs(String(w.suffix(w.count - i))) {
+                    return true
+                }
+            }
+            return false
+        }
+
+        var ans = ""
+        for w in words {
+            if dfs(w) {
+                ans = w
+            }
+            trie.insert(w)
+        }
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- end -->

lcci/17.15.Longest Word/Solution.swift

@@ -0,0 +1,57 @@
+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 {
+    func longestWord(_ words: [String]) -> String {
+        var words = words.sorted(by: { $0.count < $1.count || ($0.count == $1.count && $0 > $1) })
+        let trie = Trie()
+        
+        var dfs: ((String) -> Bool)!
+        dfs = { w in
+            if w.isEmpty {
+                return true
+            }
+            for i in 1...w.count {
+                if trie.search(String(w.prefix(i))) && dfs(String(w.suffix(w.count - i))) {
+                    return true
+                }
+            }
+            return false
+        }
+        
+        var ans = ""
+        for w in words {
+            if dfs(w) {
+                ans = w
+            }
+            trie.insert(w)
+        }
+        return ans
+    }
+}