题解 | #牛群Z字型排列#

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 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return int整型二维数组
     */
    public int[][] ZLevelOrder (TreeNode root) {
        // write code here
        ArrayList<ArrayList<Integer>> res= new ArrayList<>();
        Queue<TreeNode> q=new ArrayDeque<>();
        if(root==null){
            return new int[0][];

        }
        q.add(root);
        boolean flag=false;
        while(!q.isEmpty()){
           ArrayList<Integer> row =new ArrayList<>();
           int n=q.size();
           for(int i=0;i<n;i++){
            TreeNode cur=q.poll();
            row.add(cur.val);
            if(cur.left!=null){
                q.add(cur.left);
            }
            if(cur.right!=null){
                q.add(cur.right);
            }
           }
           if(flag==true){
            Collections.reverse(row);
            res.add(row);
            flag=!flag;
           }else{
            res.add(row);
             flag=!flag;
           }
        }
       int[][] ans = new int[res.size()][];
        for (int i = 0; i < res.size(); i++) {
            int[] arr = new int[res.get(i).size()];
            for (int j = 0; j < res.get(i).size(); j++) {
                arr[j] = res.get(i).get(j);
            }
            ans[i] = arr;
        }
        return ans;
    }
}