implement trie prefix tree solution

Author: Jeongwon Na

implement-trie-prefix-tree/njngwn.java

@@ -0,0 +1,65 @@
+// Time Complexity: O(n), n: word.length()
+// Space Complexity: O(n), n: word.length()
+class Trie {
+    private static class TrieNode {
+        HashMap<Character, TrieNode> trieNodeMap;
+        boolean isEnd;
+
+        private TrieNode() {
+            this.trieNodeMap = new HashMap<>();
+            this.isEnd = false;
+        }
+    }
+
+    private TrieNode rootNode;
+
+    public Trie() {
+        this.rootNode = new TrieNode();
+    }
+
+    public void insert(String word) {
+        TrieNode currentNode = this.rootNode;
+
+        for (char ch : word.toCharArray()) {
+            if (!currentNode.trieNodeMap.containsKey(ch)) {
+                currentNode.trieNodeMap.put(ch, new TrieNode());
+            }
+            currentNode = currentNode.trieNodeMap.get(ch);
+        }
+        currentNode.isEnd = true;
+    }
+
+    public boolean search(String word) {
+        TrieNode currentNode = this.rootNode;
+
+        for (char ch : word.toCharArray()) {
+            if (!currentNode.trieNodeMap.containsKey(ch)) {
+                return false;
+            }
+            currentNode = currentNode.trieNodeMap.get(ch);
+        }
+
+        return currentNode.isEnd;
+    }
+
+    public boolean startsWith(String prefix) {
+        TrieNode currentNode = this.rootNode;
+
+        for (char ch : prefix.toCharArray()) {
+            if (!currentNode.trieNodeMap.containsKey(ch)) {
+                return false;
+            }
+            currentNode = currentNode.trieNodeMap.get(ch);
+        }
+
+        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);
+ */