怎么回事

#pragma GCC optimize(3,"Ofast","inline")
#include <bits/stdc++.h>
using namespace std;
int n,a[30][30];
int main()
{
	cin >> n;
	int x = 1,y = n / 2 + 1,cnt = 0;
	while (cnt < n * n)
	{
		if (a[x][y] == 0)
		{
			cnt++;
			a[x][y] = cnt;
		}
		else
		{
			y--;
			if (y == 0)
			{
				y = n;
			}
			x++;
			if (x == n + 1)
			{
				x = 1;
			}
			if (a[x][y] == 0)
			{
				cnt++;
				a[x][y] = cnt;
			}
			else
			{
				y++;
				if (y == n + 1)
				{
					y = 1;
				}
				x--;
				if (x == 0)
				{
					x = n;
				}
				cnt++;
				a[x][y] = cnt;
			}
		}
	}
	for (int i = 1;i <= n;i++)
	{
		for (int j = 1;j <= n;j++)
		{
			cout << a[i][j] << " ";
		}
		cout << endl;
	}
	return 0;
}

输入：3
输出：0 1 0
      2 0 0  
      0 0 9