1つの二叉木の各層のノードの個数を求めます

import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class Test4 {
    public static void main(String[] args) {

        /*
            A
           / \
          B   C
         /   / \
        D   E   F
             \
              G
        */
        Node A = new Node(null, null, "A");
        Node B = new Node(null, null, "B");
        Node C = new Node(null, null, "C");
        Node D = new Node(null, null, "D");
        Node E = new Node(null, null, "E");
        Node F = new Node(null, null, "F");
        Node G = new Node(null, null, "G");

        A.left = B;
        A.right = C;
        B.left = D;
        C.left = E;
        C.right = F;
        E.right = G;

        Map res = getRes(A);
        System.out.println("    ：" + res.size());
        Set> entrySet = res.entrySet();
        for (Entry entry : entrySet) {
            System.out.println(entry.getKey() + " : " + entry.getValue());
        }
    }
    public static Map getRes(Node node){
        Map res = new HashMap<>();
        LinkedList currQueue = new LinkedList<>();
        LinkedList nextQueue = null;
        currQueue.addLast(node);
        int index = 1;
        int count = 1;
        res.put(index++, count);
        while(!currQueue.isEmpty()){
            nextQueue = new LinkedList<>();
            count = 0;
            while(!currQueue.isEmpty()){
                Node n = currQueue.getFirst();
                currQueue.removeFirst();
                if(n.left != null){
                    count++;
                    nextQueue.addLast(n.left);
                }
                if(n.right != null){
                    count++;
                    nextQueue.addLast(n.right);
                }
            }
            if(count > 0){
                res.put(index++, count);
            }
            currQueue = nextQueue;
        }
        return res;
    }
}
class Node{
    Node left;
    Node right;
    String data;
    public Node(Node left, Node right, String data) {
        super();
        this.left = left;
        this.right = right;
        this.data = data;
    }
}