60.把二叉樹打印成多行

題目描述

從上到下按層打印二叉樹，同一層結點從左至右輸出。每一層輸出一行。

題目解答

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;
        }
        Queue<TreeNode> queue=new LinkedList<>();
        ArrayList<Integer> list=new ArrayList<>();
        int start=0,end=1;
        queue.offer(pRoot);
        while(!queue.isEmpty()){
            TreeNode cur=queue.poll();
            list.add(cur.val);
            start++;
            if(cur.left!=null){
                queue.offer(cur.left);
            }
            if(cur.right!=null){
                queue.offer(cur.right);
            }
            if(start==end){
                end=queue.size();
                start=0;
                res.add(list);
                list=new ArrayList<Integer>();
            }
        }
        return res;
    }
}