按层遍历打印二叉树(分层) -- 漫漫算法路 刷题篇

import java.util.*;

/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}*/
public class TreePrinter {
public int[][] printTree(TreeNode root) {
// write code here
ArrayList<ArrayList<Integer>> alllist = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> list = new ArrayList<Integer>();
LinkedList<TreeNode> que = new LinkedList<TreeNode>();
if(root == null){
return null;
}
TreeNode last = root;
TreeNode nlast = last;
TreeNode node = null;
que.add(root);
while(!que.isEmpty()){
node = que.poll();
list.add(node.val);
if(node.left!=null){
que.add(node.left);
nlast=node.left;
}
if(node.right!=null){
que.add(node.right);
nlast=node.right;
}
if(node==last){
alllist.add(list);
last=nlast;
list=new ArrayList<Integer>();
}
}
int[][] res = new int[alllist.size()][];
for(int i=0;i<alllist.size();i++){
res[i] = new int[alllist.get(i).size()];
for(int j=0;j<alllist.get(i).size();j++)
res[i][j] = alllist.get(i).get(j);
}
return res;
}
}