蛇形填数（算法竞赛入门经典）

#include<iostream>
#include<vector>
#include<algorithm>
#define max 20
using namespace std;
int a[max][max];
int main()
{
	int x, y, n, tot = 0;
	cin >> n;
	memset(a, 0, sizeof(a));
	tot = a[x = 0][y = n - 1] = 1;
	while (tot<n*n)
	{
		while (x + 1 < n&&!a[x + 1][y]) a[++x][y] = ++tot;
		while (y - 1 >= 0 && !a[x][y - 1]) a[x][--y] = ++tot;
		while (x - 1>=0 && !a[x - 1][y])a[--x][y] = ++tot;
		while (y + 1 < n&&!a[x][y + 1]) a[x][++y] = ++tot;

	}
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < n; j++)
		{
			cout << a[i][j] << " ";
		}
		cout << endl;
	}
	
	system("pause");
	return 0;
}