레벨탐색(BFS)

풀이>

import java.util.LinkedList;
import java.util.Queue;
class Node {
    int data;
    Node lt, rt;
    public Node(int val) {
        data = val;
        lt=rt=null;
    }
}
public class Main {
    Node root;
    public void BFS(Node root) {
        Queue<Node> Q = new LinkedList<>();
        Q.offer(root);
        int L = 0;
        while (!Q.isEmpty()) {
            int len = Q.size();
            System.out.print(L+" : ");
            for (int i = 0; i < len; i++) {
                Node cur = Q.poll();
                System.out.print(cur.data+" ");
                if (cur.lt != null) Q.offer(cur.lt);
                if (cur.rt != null) Q.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);
        tree.BFS(tree.root);
    }
}