剑指offer-面试题23-从上往下打印二叉树

二叉树定义：

package case23_PrintFromTopToBottom;

/**
* 二叉树节点
*
* @author WangSai
*
*/
public class myTreeNode {
int data;
myTreeNode lchild;
myTreeNode rchild;

public myTreeNode() {
}

public myTreeNode(int data) {
this.data = data;
}
}


代码实现：

package case23_PrintFromTopToBottom;

/**
* 题目：从上往下打印出二叉树的每个节点，同一层的节点按照从左到右的顺序打印。例如，输入下图中的二叉树，则一次打印出8,6,10,5,7,9,11.
*
* 8
* / \
* 6 10
* / \ / \
* 5 7 9 11
*
*/
import java.util.ArrayDeque;

public class PrintFromTopToBottom {

/**
* 层序遍历二叉树
*
* @param 输入二叉树根结点
* @return
*/
public void printTree(myTreeNode headNode) {

// 异常值检测
// 打印头结点，并且把左右子节点先后放入队列中。
// 出队，打印当前的节点（根节点的左孩子），并且把当前节点的左右子节点入队。
// 继续出队，打印当前的节点（根节点的右孩子），并且把当前节点的左右子节点入队。

// 异常值检测
if (headNode == null)
return;
// 创建队列容器
ArrayDeque<myTreeNode> myQueue = new ArrayDeque<>();
// 根节点入队。
myQueue.offer(headNode);
while (!myQueue.isEmpty()) {
// 队列第一个元素出队，并且打印数据。
myTreeNode tempNode = myQueue.poll();
System.out.print(tempNode.data + " ");
// 若子节点不为null，则继续入队。
if (tempNode.lchild != null)
myQueue.offer(tempNode.lchild);
if (tempNode.rchild != null)
myQueue.offer(tempNode.rchild);
}
}

public static void main(String[] args) {
// 满二叉树
test1();
// 只有右子节点二叉树
test2();
// 只有左子节点二叉树
test3();
}

// 满二叉树
private static void test1() {
PrintFromTopToBottom pfttb = new PrintFromTopToBottom();
myTreeNode headNode = new myTreeNode(8);
myTreeNode N1 = new myTreeNode(6);
myTreeNode N2 = new myTreeNode(10);
myTreeNode N3 = new myTreeNode(5);
myTreeNode N4 = new myTreeNode(7);
myTreeNode N5 = new myTreeNode(9);
myTreeNode N6 = new myTreeNode(11);
headNode.lchild = N1;
headNode.rchild = N2;
N1.lchild = N3;
N1.rchild = N4;
N2.lchild = N5;
N2.rchild = N6;
pfttb.printTree(headNode);
System.out.println();
}

// 只有右子节点二叉树
private static void test2() {
PrintFromTopToBottom pfttb = new PrintFromTopToBottom();
myTreeNode headNode = new myTreeNode(8);
myTreeNode N2 = new myTreeNode(10);
myTreeNode N6 = new myTreeNode(11);
headNode.rchild = N2;
N2.rchild = N6;
pfttb.printTree(headNode);
System.out.println();
}

// 只有左子节点二叉树
private static void test3() {
PrintFromTopToBottom pfttb = new PrintFromTopToBottom();
myTreeNode headNode = new myTreeNode(8);
myTreeNode N1 = new myTreeNode(6);
myTreeNode N3 = new myTreeNode(5);
headNode.lchild = N1;
N1.lchild = N3;
pfttb.printTree(headNode);
System.out.println();
}

}