从上到下按层打印二叉树，同一层结点从左至右输出。每一层输出一行。
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
/*
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>> res=new ArrayList<>();
if(pRoot==null){
return res;
}
ArrayList<Integer> list = new ArrayList<>();
Queue<TreeNode> queue=new LinkedList<>();
queue.offer(pRoot);
while(!queue.isEmpty()){
list = new ArrayList<>();
int size = queue.size();
for(int i=0;i<size;i++){
TreeNode temp = queue.poll();
if(temp.left!=null){
queue.add(temp.left);
}
if(temp.right!=null){
queue.add(temp.right);
}
list.add(temp.val);
}
res.add(list);
}
return res;
}
}