剑指offer032.1从上往下打印二叉树

Problem:

从上往下打印出二叉树的每个节点，同层节点从左至右打印。

Intuition:

要实现按层打印，只需要将左右节点存到一个队列里面，按顺序打印即可

Solution:

public class CodingInterview_032 {
    class TreeNode{
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val){
            this.val=val;
        }
    }


    public class Solution {
        public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
            ArrayList<Integer> list = new ArrayList<>();
            ArrayList<TreeNode> queue = new ArrayList<>();
            if (root == null) {
                return list;
            }
            queue.add(root);
            while (queue.size() != 0) {
                TreeNode temp = queue.remove(0);
                if (temp.left != null){
                    queue.add(temp.left);
                }
                if (temp.right != null) {
                    queue.add(temp.right);
                }
                list.add(temp.val);
            }
            return list;
        }
    }
}