d.cpp

ACM训练题解 最新版 共8题 ACM训练题解 最新版 共8题

// Problem D
// http://acm.sgu.ru/problem.php?contest=0&problem=222
// Solution by semiconductor
#include	<cstdio>

int C[11][11];
int F[11];

void
Gen(void)
{
	for ( int i = 0; i <= 10; i++ ) {
		C[i][0] = 1;
		for ( int j = 1; j <= i; j++ ) 
			C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
	}
	F[0] = 1;
	for ( int i = 1; i <= 10; i++ ) F[i] = F[i - 1] * i;
}

int
main()
{
	Gen();
	int n, k;
	while ( scanf("%d %d", &n, &k) != EOF ) {
		int res;
		if ( k > n ) res = 0;
		else {
			res = C[n][k] * C[n][k] * F[k];
		}
		printf("%d\n", res);
	}
}