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<>();
        if(pRoot == null) return res;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(pRoot);
        boolean flag = true;
        while(!q.isEmpty()){
            ArrayList<Integer> temp = new ArrayList<>();
            int len = q.size();
            for(int i = 0; i < len; i++){
                TreeNode cur = q.poll();
                temp.add(cur.val);
                if(cur.left != null) q.offer(cur.left);
                if(cur.right != null) q.offer(cur.right);
            }
            if(!flag) Collections.reverse(temp);
            res.add(temp);
            flag = !flag;
        }
        return res;
    }

}