题解 | #把二叉树打印成多行#

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 {
    ArrayList<ArrayList<Integer> > Print(TreeNode root) {
        ArrayList<ArrayList<Integer>> ans = new ArrayList<>();
        if(root == null) {
            return ans;
        }
        LinkedList<TreeNode> queue = new LinkedList<>();
        queue.addLast(root);
        while(!queue.isEmpty()) {
            int sz = queue.size();
            ArrayList<Integer> lvl = new ArrayList<>();
            for(int i = 0; i < sz; i++) {
                TreeNode tmp = queue.removeFirst();
                lvl.add(tmp.val);
                if(tmp.left != null)  queue.addLast(tmp.left);
                if(tmp.right != null) queue.addLast(tmp.right);
            }
            ans.add(lvl);
        }
        return ans;
    }
    
}