剑指59.按之字形顺序打印二叉树

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

/*
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> > ans = new ArrayList<>();
        if (pRoot == null) return ans;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(pRoot);
        int level = 1; // 记录层数
        while (!queue.isEmpty()){
            int levelNums = queue.size();
            ArrayList<Integer> list = new ArrayList<>();
            for (int i = 0; i < levelNums; i++) {
                TreeNode cur = queue.poll();
                if ((level & 1) == 1){ // 奇数层
                    list.add(cur.val);
                }else{  // 偶数层
                    list.add(0,cur.val);
                }
                if (cur.left != null) queue.offer(cur.left);
                if (cur.right != null) queue.offer(cur.right);
            }
            level++;
            ans.add(list);
        }
        return ans;
    }
}