[luoguP2401] 不等数列

#include <cstdio>
#define N 1001
#define p 2015

int n, k;
int f[N][N];

int main()
{
	int i, j;
	scanf("%d %d", &n, &k);
	f[2][0] = 1;
	f[2][1] = 1;
	for(i = 3; i <= n; i++)
		for(j = 0; j < i; j++)
		{
			//插头 
			f[i][j] = (f[i][j] + f[i - 1][j]) % p;
			//插尾
			if(j) f[i][j] = (f[i][j] + f[i - 1][j - 1]) % p;
			//插中间 
			//替换 <
			f[i][j] = (f[i][j] + f[i - 1][j] * j % p) % p;
			//替换 >
			if(j) f[i][j] = (f[i][j] + f[i - 1][j - 1] * (i - j - 1) % p) % p; 
		}
	printf("%d\n", f[n][k]);
	return 0;
}