蛇形填数

10  11  12  1
9   16   13  2
8   15   14  3
7    6    5   4

#include<stdio.h>
#include<string.h>
#define maxn 20
int a[maxn][maxn];
int main(){
	int n,x,y,tot=0;
	scanf("%d",&n);
	memset(a,0,sizeof(a));
	tot = a[x=0][y=n-1]=1;//通过观察样例可得知。 
	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+1] = tot++;
	}
	for(x =0;x<n;x++)
	{
		for(y=0;y<n;y++)   printf("%3d",a[x][y]);
		printf("\n");
	}
	return 0;
}