Recursive, Tree, Graph(DFS, BFS 기초) - 이진트리 레벨탐색(BFS : Breadth-First Search)

import java.util.LinkedList;
import java.util.Queue;

class Node {
    int data;
    Node lt;
    Node rt;

    public Node(int data) {
        this.data = data;
        this.lt = null;
        this.rt = null;
    }
}

public class Main {
    private Node root;

    public static void BFS(Node root) {
        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);
        int L = 0;
        while (!queue.isEmpty()) {
            int len = queue.size();
            System.out.print(L + " : ");
            for (int i = 0; i < len; i++) {
                Node cur = queue.poll();
                System.out.print(cur.data + " ");
                if (cur.lt != null) queue.offer(cur.lt);
                if (cur.rt != null) queue.offer(cur.rt);
            }
            L++;
            System.out.println();
        }
    }

    public static void main(String[] args) {
        Main tree = new Main();
        tree.root = new Node(1);
        tree.root.lt = new Node(2);
        tree.root.rt = new Node(3);
        tree.root.lt.lt = new Node(4);
        tree.root.lt.rt = new Node(5);
        tree.root.rt.lt = new Node(6);
        tree.root.rt.rt = new Node(7);
        BFS(tree.root);
    }
}

- 레벨 탐색 순회 출력 : 1 2 3 4 5 6 7

0 : 1 
1 : 2 3 
2 : 4 5 6 7 

이런식으로 탐색된다.