解法一：分隔节点

import java.util.*;
/*
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 pRoot) {
        Queue<TreeNode> q=new LinkedList<>();
        ArrayList<ArrayList<Integer>> ans=new ArrayList<>();
        ArrayList<Integer> l=new ArrayList<>();
        if(pRoot==null) {
           return ans;
        }
        q.add(pRoot);
        TreeNode split=new TreeNode(0);
        q.add(split);
        while(q.size()!=1){
            TreeNode curr=q.poll();
            if(curr==split){
                ans.add(l);
                l=new ArrayList<>();
                q.add(split);
                continue;
            }
            l.add(curr.val);
            if(curr.left!=null) q.add(curr.left);
            if(curr.right!=null) q.add(curr.right);
        }
        if(l.size()!=0) ans.add(l);
        return ans;
    }    
}

解法二：BFS+记录深度

import java.util.*;
/*
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 pRoot) {
        ArrayList<ArrayList<Integer>> ans=new ArrayList<>();
        if(pRoot==null) return ans;
        Queue<TreeNode> q=new LinkedList<>();
        q.add(pRoot);
        int level=0;
        while(!q.isEmpty()){
            ans.add(new ArrayList<Integer>());
            int size=q.size();
            while(size-->0){
                TreeNode curr=q.poll();
                ans.get(level).add(curr.val);
                if(curr.left!=null) q.add(curr.left);
                if(curr.right!=null) q.add(curr.right);
            }
            level++;
        }
        return ans;
    }

}

解法三：DFS+记录深度

略