题解 | #按之字形顺序打印二叉树#

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Collections;

/*
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> queue = new LinkedList<>();
        boolean flag = true;
        queue.add(pRoot);
        while (!queue.isEmpty()) {
            Queue<TreeNode> temp = new LinkedList<>();
            ArrayList<Integer> arrayList = new ArrayList<>();
            while (!queue.isEmpty()) {
                arrayList.add(queue.peek().val);
                if (queue.peek().left != null) {
                    temp.add(queue.peek().left);
                }
                if (queue.peek().right != null) {
                    temp.add(queue.peek().right);
                }
                queue.poll();
            }
            if (!flag) {
                Collections.reverse(arrayList);
            }
            flag = !flag;
            while (!temp.isEmpty()) {
                queue.add(temp.poll());
            }
            res.add(arrayList);
        }
        return res;
    }

}