剑指offer-从上往下打印二叉树

import java.util.ArrayList;
import java.util.LinkedList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> list =new ArrayList<>();
        //空格的情况直接返回
        if(root == null){
            return list;
        }
        LinkedList<TreeNode> mas =new LinkedList<>();
        //压入主队列根节点
        mas.add(root);
        while(!mas.isEmpty()){
            //每一次循环，将当前节点的子节点加到队列的尾部。
            while(!mas.isEmpty()){
                TreeNode node = mas.pop();
                list.add(node.val);
                if(node.left != null){
                    mas.add(node.left);
                }
                if(node.right != null){
                    mas.add(node.right);
                }
            }
        }
        return list;
    }
}

import java.util.ArrayList;
import java.util.LinkedList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> list =new ArrayList<>();
        //空格的情况直接返回
        if(root == null){
            return list;
        }
        //主队列和辅助队列
        LinkedList<TreeNode> mas =new LinkedList<>();
        LinkedList<TreeNode> fz =new LinkedList<>();
        //压入主队列根节点
        mas.add(root);
        while(!mas.isEmpty()){
            //每一次循环，将主队列代表的一行记录加到list中，并将下一行记录到辅助队列
            while(!mas.isEmpty()){
                TreeNode node = mas.pop();
                list.add(node.val);
                if(node.left != null){
                    fz.add(node.left);
                }
                if(node.right != null){
                    fz.add(node.right);
                }
            }
            //将辅助队列的一行记录加到主队列中
            while(!fz.isEmpty()){
                mas.add(fz.pop());
            }
        }
        return list;
    }
}