implement trie prefix tree

Author: se6816

implement-trie-prefix-tree/se6816.java

@@ -0,0 +1,92 @@
+/**
+	연결 리스트를 통해, 트리 구조를 만들고 탐색하는 방식
+*/
+class Trie {
+    public Map<Character, WordNode> wordMap;
+
+    public Trie() {
+        wordMap = new HashMap<>();
+    }
+    
+    public void insert(String word) {
+        WordNode wordNode = null;
+        char ch = word.charAt(0);
+        wordNode = wordMap.get(ch);
+
+        if(wordNode == null) {
+            boolean isFirstWord = word.length() == 1;
+            wordNode = new WordNode(ch, isFirstWord);
+            wordMap.put(ch, wordNode);
+        }
+
+        for(int idx = 1; idx < word.length(); idx++) {
+            char target = word.charAt(idx);
+            boolean isLeaf = word.length() - 1 == idx;
+            wordNode = wordNode.next.computeIfAbsent(target, key -> new WordNode(key, isLeaf));
+        }
+        wordNode.isLeaf = true;
+    }
+    
+    public boolean search(String word) {
+        
+        WordNode wordNode = null;
+        char ch = word.charAt(0);
+        wordNode = wordMap.get(ch);
+        if (wordNode == null) return false;
+        
+        
+        for(int idx = 1; idx < word.length(); idx++) {
+            char target = word.charAt(idx);
+            if (!wordNode.next.containsKey(target)) {
+                return false;
+            }
+            wordNode = wordNode.next.get(target);
+        }
+
+        return wordNode.isLeaf;
+    }
+    
+    public boolean startsWith(String word) {
+        
+        WordNode wordNode = null;
+        char ch = word.charAt(0);
+        wordNode = wordMap.get(ch);
+        if (wordNode == null) return false;
+        
+        
+        for(int idx = 1; idx < word.length(); idx++) {
+            char target = word.charAt(idx);
+            if (!wordNode.next.containsKey(target)) {
+                return false;
+            }
+            wordNode = wordNode.next.get(target);
+        }
+
+        return true;
+    }
+}
+
+class WordNode {
+    char ch;
+    Map<Character, WordNode> next;
+    boolean isLeaf;
+
+    public WordNode(char ch) {
+        this(ch, false);
+    }
+    
+    public WordNode(char ch, boolean isLeaf) {
+        next = new HashMap<>();
+        this.ch = ch;
+        this.isLeaf = isLeaf;
+    }
+
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * Trie obj = new Trie();
+ * obj.insert(word);
+ * boolean param_2 = obj.search(word);
+ * boolean param_3 = obj.startsWith(prefix);
+ */