题解 | #按之字形顺序打印二叉树#

import java.util.*;

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        if(pRoot==null){
            return res;
        }
        Queue<TreeNode> q = new LinkedList<>();
        q.add(pRoot);
        int j = 1;
        while(!q.isEmpty()){
            ArrayList<Integer> list = new ArrayList<>();
            int n = q.size();
            for(int i = 0 ; i < n ;i++){
                TreeNode node = q.poll();
                list.add(node.val);
                if(node.left!=null){
                    q.add(node.left);
                }
                if(node.right!=null){
                    q.add(node.right);
                }
            }
            if(j%2==0){
                Collections.reverse(list);
            }
            j++;
            res.add(list);
        }
        return res;
    }

}