Add a solution to Search Suggestions System

Author: soapyigu

Design/SearchSuggestionsSystem.swift

@@ -0,0 +1,72 @@
+/**
+ * Question Link: https://leetcode.com/problems/search-suggestions-system/
+ * Primary idea: Use trie to add and search prefix (DFS).
+ *
+ * Time Complexity: O(n), Space Complexity: O(n)
+ *
+ */
+
+class SearchSuggestionsSystem {
+    func suggestedProducts(_ products: [String], _ searchWord: String) -> [[String]] {
+        let trie = Trie()
+        var res = [[String]]()
+    
+        products.forEach { trie.insert($0) }
+        
+        return (1...searchWord.count).map { trie.searchWords(for: String(searchWord.prefix($0))) }
+    }
+    
+    private class Trie {
+        let root = TrieNode()
+        
+        func insert(_ word: String) {
+            var node = root
+            
+            for char in word {
+                if node.charNodeMap[char] == nil {
+                    node.charNodeMap[char] = TrieNode()
+                }
+                    
+                node = node.charNodeMap[char]!
+            }
+            
+            node.isWord = true
+        }
+        
+        func searchWords(for term: String) -> [String] {
+            var res = [String](), node = root
+            
+            for char in term {
+                guard let next = node.charNodeMap[char] else {
+                    return res
+                }
+                
+                node = next
+            }
+            
+            dfs(&res, term, node)
+            
+            return Array(res.sorted().prefix(3))
+        }
+        
+        private func dfs(_ res: inout [String], _ path: String, _ node: TrieNode) {
+            if node.isWord {
+                res.append(path)
+            }
+            
+            for (char, next) in node.charNodeMap {
+                dfs(&res, path + String(char), next)
+            }
+        }
+    }
+    
+    private class TrieNode {
+        var isWord: Bool
+        var charNodeMap: [Character: TrieNode]
+        
+        init() {
+            isWord = false
+            charNodeMap = [Character: TrieNode]()
+        }
+    }
+}