题解 | #把二叉树打印成多行#

import java.util.ArrayList;

import java.util.ArrayDeque;

public class Solution {

ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
    ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
    if(pRoot==null)
        return res;
    //层次遍历
    ArrayDeque<TreeNode> dq = new ArrayDeque<>();
    dq.addLast(pRoot);
    while(!dq.isEmpty()){
        ArrayList<Integer> arr = new ArrayList<>();
        int curSize = dq.size();
        while(curSize-->0){
            TreeNode node = dq.pollFirst();
            arr.add(node.val);
            if(node.left!=null) dq.addLast(node.left);
            if(node.right!=null) dq.addLast(node.right);
        }
        res.add(arr);
    }
    return res;
}

}