From 279413a350a8ecfd255cbc8f5494ba224addbf83 Mon Sep 17 00:00:00 2001
From: Uday Vig <uday.vig@gmail.com>
Date: Wed, 4 Oct 2017 18:51:40 +0530
Subject: [PATCH] Added Trie Implementation in Java

Contains functions like add a word, remove a word, search for a particular word, etc.
---
 data_structures/Trie/Trie.java | 122 +++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 data_structures/Trie/Trie.java

diff --git a/data_structures/Trie/Trie.java b/data_structures/Trie/Trie.java
new file mode 100644
index 000000000000..d3af6f6e5307
--- /dev/null
+++ b/data_structures/Trie/Trie.java
@@ -0,0 +1,122 @@
+package lecture20;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+public class Trie {
+	private class Node {
+		Character data;
+		HashMap<Character, Node> children;
+		boolean isTerminal;
+
+		public Node(Character data, boolean isTerminal) {
+			this.data = data;
+			this.children = new HashMap<>();
+			this.isTerminal = isTerminal;
+		}
+	}
+
+	private Node root;
+	private int numWords;
+
+	public Trie() {
+		this.root = new Node('\0', false);
+		this.numWords = 0;
+	}
+
+	public int getNumWords() {
+		return this.numWords;
+	}
+
+	public void display() {
+		this.display(this.root, "");
+	}
+
+	private void display(Node node, String osf) {
+		if (node.isTerminal) {
+			String toprint= osf.substring(1) + node.data;
+		//	osf = osf.substring(1);
+			System.out.println(toprint);
+		}
+
+		Set<Map.Entry<Character, Node>> entries = node.children.entrySet();
+		for (Map.Entry<Character, Node> entry : entries) {
+			this.display(entry.getValue(), osf + node.data);
+		}
+	}
+
+	public void add(String word) {
+		this.add(this.root, word);
+	}
+
+	private void add(Node node, String word) {
+		if (word.length() == 0) {
+			if (!node.isTerminal) {
+				node.isTerminal = true;
+				this.numWords++;
+			}
+			return;
+		}
+		if (node.children.get(word.charAt(0)) == null) {
+			Node n = new Node(word.charAt(0), false);
+			node.children.put(word.charAt(0), n);
+		}
+		this.add(node.children.get(word.charAt(0)), word.substring(1));
+	}
+	
+	public boolean search(String word){
+		return this.search(this.root,word);
+	}
+	
+	private boolean search(Node node,String word){
+		if (word.length() == 0) {
+			if (node.isTerminal) {
+				return true;
+			}else{
+				return false;
+			}
+		}
+		if (node.children.get(word.charAt(0)) == null) {
+			return false;
+		}
+		return this.search(node.children.get(word.charAt(0)), word.substring(1));
+	}
+	
+	public void displayAsTree(){
+		this.displayAsTree(this.root);
+	}
+	
+	private void displayAsTree(Node node){
+		System.out.print(node.data+"=>");
+		Set<Map.Entry<Character, Node>> entries = node.children.entrySet();
+		for (Map.Entry<Character, Node> entry : entries) {
+			System.out.print((entry.getKey()+", "));
+		}
+		System.out.println("END");
+		for (Map.Entry<Character, Node> entry : entries) {
+			this.displayAsTree(entry.getValue());
+		}
+	}
+	
+	public void remove(String word){
+		this.remove(this.root,word);
+	}
+	
+	private void remove(Node node,String word){
+		if (word.length() == 0) {
+			if (node.isTerminal) {
+				node.isTerminal=false;
+				this.numWords--;
+			}
+			return;
+		}
+		if (node.children.get(word.charAt(0)) == null) {
+			return;
+		}
+		this.remove(node.children.get(word.charAt(0)), word.substring(1));
+		if(!node.children.get(word.charAt(0)).isTerminal&&node.children.size()==0){
+			node.children.remove(word.charAt(0));
+		}
+	}
+}