题解 | #按之字形顺序打印二叉树#

import java.util.ArrayList;
import java.util.LinkedList;

public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        if (pRoot == null) return list;
        LinkedList<TreeNode> queue = new LinkedList<>();
        int levelflag = 1;
        queue.offer(pRoot);
        while (!queue.isEmpty()) {
            ArrayList<Integer> level = new ArrayList<>();
            LinkedList<TreeNode> temp = new LinkedList<>();
            temp.addAll(queue);
            int num = queue.size();
            if (levelflag % 2 == 0) {
                for (int i = 0 ; i < num; i++) {
                    TreeNode p = temp.getLast();
                    if (p.right != null) {
                        queue.offer(p.right);
                    }
                    if (p.left != null) {
                        queue.offer(p.left);
                    }
                    level.add(p.val);
                    queue.remove(p);
                    temp.removeLast();
                }
            } else {
                for (int i = 0 ; i < num; i++) {
                    TreeNode p = temp.getLast();
                    if (p.left != null) {
                        queue.offer(p.left);
                    }
                    if (p.right != null) {
                        queue.offer(p.right);
                    }
                    level.add(p.val);
                    queue.remove(p);
                    temp.removeLast();
                }
            }
            list.add(level);
            levelflag++;
        }
        return list;
    }
}