# 把二叉树打印出多行

## 题目：从上到下按层打印二叉树，同一层的结点按从左到右的顺序打印，每一层打印一行。

### 结点定义

private static class BinaryTreeNode {
private int val;
private BinaryTreeNode left;
private BinaryTreeNode right;
public BinaryTreeNode() {
}
public BinaryTreeNode(int val) {
this.val = val;
}
@Override
public String toString() {
return val + "";
}
}

### 代码实现

import java.util.LinkedList;
import java.util.List;
public class Test60 {
private static class BinaryTreeNode {
private int val;
private BinaryTreeNode left;
private BinaryTreeNode right;
public BinaryTreeNode() {
}
public BinaryTreeNode(int val) {
this.val = val;
}
@Override
public String toString() {
return val + "";
}
}
/**
* 题目：从上到下按层打印二叉树，同一层的结点按从左到右的顺序打印，每一层打印一行。
* @param root
*/
public static void print(BinaryTreeNode root) {
if (root == null) {
return;
}
BinaryTreeNode node;
// 当前层的结点个数
int current = 1;
// 记录下一层的结点个数
int next = 0;
while (list.size() > 0) {
node = list.remove(0);
current--;
System.out.printf("%-3d", node.val);
if (node.left != null) {
next++;
}
if (node.right != null) {
next++;
}
if (current ==0) {
System.out.println();
current = next;
next = 0;
}
}
}
public static void main(String[] args) {
BinaryTreeNode n1 = new BinaryTreeNode(1);
BinaryTreeNode n2 = new BinaryTreeNode(2);
BinaryTreeNode n3 = new BinaryTreeNode(3);
BinaryTreeNode n4 = new BinaryTreeNode(4);
BinaryTreeNode n5 = new BinaryTreeNode(5);
BinaryTreeNode n6 = new BinaryTreeNode(6);
BinaryTreeNode n7 = new BinaryTreeNode(7);
BinaryTreeNode n8 = new BinaryTreeNode(8);
BinaryTreeNode n9 = new BinaryTreeNode(9);
n1.left = n2;
n1.right = n3;
n2.left = n4;
n2.right = n5;
n3.left = n6;
n3.right = n7;
n4.left = n8;
n4.right = n9;
print(n1);
}
}