面试题32：从上到下打印二叉树
题目要求：
从上到下打印二叉树的每个节点，同一层的节点按照从左到右的顺序打印。
解题思路：
这道题就是二叉树的层序遍历。使用一个队列，进行广度优先遍历即可。
package structure;
import java.util.LinkedList;
import java.util.Queue;
/**
* Created by ryder on 2017/6/12.
* 树节点
*/
public class TreeNode<T> {
public T val;
public TreeNode<T> left;
public TreeNode<T> right;
public TreeNode(T val){
this.val = val;
this.left = null;
this.right = null;
}
}
package chapter4;
import structure.TreeNode;
import java.util.LinkedList;
import java.util.Queue;
/**
* Created by ryder on 2017/7/17.
* 从上到下打印二叉树(层序遍历)
*/
public class P171_PrintTreeFromTopToBottom {
public static void printFromTopToBottom(TreeNode<Integer> root){
if(root==null)
return;
Queue<TreeNode<Integer>> queue = new LinkedList<>();
queue.offer(root);
TreeNode<Integer> temp;
while(!queue.isEmpty()){
temp = queue.poll();
System.out.print(temp.val);
System.out.print('\t');
if(temp.left!=null)
queue.offer(temp.left);
if(temp.right!=null)
queue.offer(temp.right);
}
}
public static void main(String[] args){
// 1
// / \
// 2 3
// / \ / \
// 4 5 6 7
TreeNode<Integer> root = new TreeNode<Integer>(1);
root.left = new TreeNode<Integer>(2);
root.right = new TreeNode<Integer>(3);
root.left.left = new TreeNode<Integer>(4);
root.left.right = new TreeNode<Integer>(5);
root.right.left = new TreeNode<Integer>(6);
root.right.right = new TreeNode<Integer>(7);
printFromTopToBottom(root);
}
}
运行结果
1 2 3 4 5 6 7
