implement-trie-prefix-tree solutions

Author: hyeri0903

implement-trie-prefix-tree/hyeri0903.java

@@ -0,0 +1,68 @@
+class Trie {
+    class TrieNode {
+        TrieNode[] children;
+        boolean isEnd;
+
+        public TrieNode() {
+            children = new TrieNode[26]; // a ~ z
+            isEnd = false;
+        }
+    }
+
+    private TrieNode root;
+
+    public Trie() {
+        root = new TrieNode();
+    }
+    
+    public void insert(String word) {
+        TrieNode node = root;
+
+        for(char c: word.toCharArray()) {
+            int index = c - 'a';
+            //처음 들어오는 단어는 node 생성
+            if(node.children[index] == null) {
+                node.children[index] = new TrieNode();
+            }
+            //다음 노드로 이동
+            node = node.children[index];
+        }
+        //단어의 끝 표시
+        node.isEnd = true;
+    }
+    
+    public boolean search(String word) {
+        TrieNode node = root;
+        for(char c: word.toCharArray()) {
+            int index = c - 'a';
+            //존재하지 않으면 false return
+            if(node.children[index] == null) {
+                return false;
+            }
+            //다음 노드로 이동
+            node = node.children[index];
+        }
+        return node.isEnd;
+    }
+    
+    public boolean startsWith(String prefix) {
+        //중간에 null을 안만나면 true 반환
+        TrieNode node = root;
+        for(char c: prefix.toCharArray()) {
+            int index = c - 'a';
+            if(node.children[index] == null) {
+                return false;
+            }
+            node = node.children[index];
+        }
+        return true;
+    }
+}
+
+/**
+ * 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);
+ */