蛇形填数（二） c++

Question

蛇形填数（二）
题目描述
给出 n×n 的方格，按照如下方式进行填数，并输出
输入
一个整数 n, n<40
输出
n 行 n 列，每行数字间用空格间隔
样例
输入数据 1
4
输出数据 1
1 2 6 7
3 5 8 13
4 9 12 14
10 11 15 16
限制
1s, 512MB 每组测试数据

#include<iostream>
using namespace std;
int main(){
    int n;
    int k=1;
    int a[1000][1000];
    cin>>n;
    for(int i=0;i<=2*n-2;i++)
    {
        for(int j=i;j>=0;j--)
        {
            if(j<n&&i-j<n)
            {
                if(i%2!=0)
                    a[i-j][j]=j++;
                else
                    a[j][i-j]=j++;
            }
        }
    }
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
               cout<<a[i][j];
        } 
        cout<<endl;
    }
}

Time Exceeded 2037.463835ms 4164KiB
foo.cc: In function 'int main()':
foo.cc:15:17: warning: operation on 'j' may be undefined [-Wsequence-point]
15 | a[i-j][j]=j++;
| ^
foo.cc:15:17: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:15:17: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:15:17: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:17:32: warning: operation on 'j' may be undefined [-Wsequence-point]
17 | a[j][i-j]=j++;
| ^
foo.cc:17:32: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:17:32: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:17:32: warning: operation on 'j' may be undefined [-Wsequence-point]
foo.cc:5:6: warning: unused variable 'k' [-Wunused-variable]
5 | int k=1;
| ^

试过去查资料

请各位帮帮忙

Answer 1

https://blog.csdn.net/technologist_37/article/details/118545970?spm=1001.2014.3001.5502