58、把二叉树打印成多行

一、题目

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。

二、解法

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>> list = new ArrayList<ArrayList<Integer>>();
        depth(pRoot,1,list);
        return list;
    }
     private void depth(TreeNode root,int depth,ArrayList<ArrayList<Integer>> list){
         if(root == null)
             return;
         if(depth > list.size())
             list.add(new ArrayList<Integer>());
         list.get(depth-1).add(root.val);
         depth(root.left,depth+1,list);
         depth(root.right,depth+1,list);
     }*/
    ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> al = new ArrayList<ArrayList<Integer>>();
        if(pRoot == null)
            return al;
        //使用队列
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(pRoot);
        while(!queue.isEmpty()){
            ArrayList<Integer> list = new ArrayList<Integer>();//存储一行
            int size = queue.size();
            int start = 0;
            while(start++ < size){
                TreeNode t = queue.poll();
                if(t.left != null)
                    queue.add(t.left);
                if(t.right != null)
                    queue.add(t.right);
                list.add(t.val);
            }
            al.add(list);
        }
        return al;
    }
    
}