feat: Solution for Problem #1032 - Stream of Characters

Author: milanpanchal

Swift/Problems/1032_StreamOfCharacters.playground/Contents.swift

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+/*:
+# 1032. Stream of Characters [Hard]
+  https://leetcode.com/problems/stream-of-characters/
+
+ ---
+
+### Problem Statement:
+
+ Implement the `StreamChecker` class as follows:
+
+ + `StreamChecker(words)`: Constructor, init the data structure with the given words.
+ + `query(letter)`: returns true if and only if for some `k >= 1`, the last `k` characters queried (in order from oldest to newest, including this letter just queried) spell one of the words in the given list.
+
+### Example:
+
+ ```
+ StreamChecker streamChecker = new StreamChecker(["cd","f","kl"]); // init the dictionary.
+ streamChecker.query('a');          // return false
+ streamChecker.query('b');          // return false
+ streamChecker.query('c');          // return false
+ streamChecker.query('d');          // return true, because 'cd' is in the wordlist
+ streamChecker.query('e');          // return false
+ streamChecker.query('f');          // return true, because 'f' is in the wordlist
+ streamChecker.query('g');          // return false
+ streamChecker.query('h');          // return false
+ streamChecker.query('i');          // return false
+ streamChecker.query('j');          // return false
+ streamChecker.query('k');          // return false
+ streamChecker.query('l');          // return true, because 'kl' is in the wordlist
+  
+ ```
+ 
+ ### Notes:
+ + 1 <= words.length <= 2000
+ + 1 <= words[i].length <= 2000
+ + Words will only consist of lowercase English letters
+ + Queries will only consist of lowercase English letters.
+ + The number of queries is at most 40000.
+ 
+ ### Hint:
+ + Put the words into a trie, and manage a set of pointers within that trie.
+
+ */
+
+// 17 / 17 test cases passed.
+// Status: Accepted
+// Runtime: 1908 ms
+// Memory Usage: 31.9 MB
+
+class Trie {
+    var endOfWord: Bool = false
+    var chars = [Character: Trie]()
+}
+
+class StreamChecker {
+    var queryStream = [Character]()
+//    var queryStream = ""
+    var root: Trie
+    
+    init(_ words: [String]) {
+        root = Trie()
+        
+        for word in words {
+            var node = root
+            for char in word.reversed() {
+                if node.chars[char] == nil {
+                    node.chars[char] = Trie()
+                }
+                node = node.chars[char]!
+            }
+            node.endOfWord = true
+        }
+    }
+    
+    func query(_ letter: Character) -> Bool {
+        queryStream.append(letter)
+//        queryStream += String(letter)
+        
+        var node = root
+        for char in queryStream.reversed() {
+            guard let next = node.chars[char] else {
+                return false
+            }
+
+            if next.endOfWord {
+                return true
+            }
+            
+            node = next
+        }
+        
+        return false
+    }
+}
+
+ // Your StreamChecker object will be instantiated and called as such:
+
+ let obj = StreamChecker(["cd","f","kl"])
+ obj.query("a")
+ obj.query("b")
+ obj.query("c")
+ obj.query("d")
+ obj.query("e")
+ obj.query("f")
+ obj.query("g")
+ obj.query("h")
+ obj.query("i")
+ obj.query("j")
+ obj.query("k")
+ obj.query("l")
+

Swift/Problems/1032_StreamOfCharacters.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>