[백준][BOJ-1991][자바] 트리 순회

 

www.acmicpc.net/problem/1991

1991번: 트리 순회

import java.util.*;
import java.io.*;

public class Main {
	static Node root;
	
	public static void main(String[] args) throws NumberFormatException, IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		int T = Integer.parseInt(br.readLine());
		HashMap<String, Node> hm = new HashMap<>();
		StringTokenizer st;
		String parents = "";
		String left = "";
		String right = "";
		
		hm.put("A", new Node("A",null,null));
		
		for(int i=0; i<T; i++) {
			st = new StringTokenizer(br.readLine());
			parents = st.nextToken();
			left = st.nextToken();
			right = st.nextToken();
			
			Node leftNode = new Node(left, null, null);
			Node rightNode = new Node(right, null, null);
			
			if(!left.equals(".")) {
				hm.get(parents).left = leftNode;
				hm.put(left, leftNode);
			}
			
			if(!right.equals(".")) {
				hm.get(parents).right = rightNode;
				hm.put(right, rightNode);
			}
		}
		
		preOrder(hm.get("A"));
		System.out.println();
		inOrder(hm.get("A"));
		System.out.println();
		postOrder(hm.get("A"));
	}
	
	public static void inOrder(Node node) {
        if(node != null) {
            inOrder(node.left);
            System.out.print(node.data);
            inOrder(node.right);
        }
    }
    
    //전위순회 Preorder = Root -> Left -> Right
    public static void preOrder(Node node) {
        if(node != null) {
            System.out.print(node.data);
            preOrder(node.left);
            preOrder(node.right);
        }
    }
    
    //후위순회 Postorder = Left -> Right -> Root
    public static void postOrder(Node node) {
        if(node != null) {
        	postOrder(node.left);
        	postOrder(node.right);
            System.out.print(node.data);
        }
    }

	static class Node {
		String data;
		Node left;
		Node right;
		public Node(String data, Node left, Node right) {
			super();
			this.data = data;
			this.left = left;
			this.right = right;
		}
	}

}