题解 | #按之字形顺序打印二叉树#

import java.util.*;
import java.util.ArrayList;

/*
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<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if(pRoot != null) queue.add(pRoot);
        while(!queue.isEmpty()) {
            LinkedList<Integer> tmp = new LinkedList<>();
            for(int i=queue.size(); i>0; i--) {
                TreeNode node = queue.poll();
                if(res.size() % 2 == 0) tmp.addLast(node.val);
                else tmp.addFirst(node.val);
                if(node.left != null) queue.add(node.left);
                if(node.right != null) queue.add(node.right);                
            }
            res.add(new ArrayList<>(tmp));
        }
        return res;
    }
}