HDU 1521 排列组合

HDU 1521 排列组合

题意：
（中文）
思路：
此题是一道指数型母函数的题目，
G(x) = (1 + x / 1! + x^2 / 2！ + x^3 / 3! + …. + x^n1 / n1!)
* (1 + x / 1 ! + x^2 / 2! + … + x^n2 / n2!) * …
* (1 + x / 1! + x^2 / 2! + .. + x^nk / nk!).
先把阶层求出来，当计算的时候每次都除f[n],在最后还原系数的时候再乘上去。
Code：

#include<cstdio>#include<cstdlib>#include<cstring>#include<cctype>#include<cmath>#include<algorithm>#include<iostream>#include<string>#include<vector>#include<bitset>#include<queue>#include<stack>#include<list>#include<map>#include<set>#define TEST#define LL long long#define Mt(f, x) memset(f, x, sizeof(f));#define rep(i, s, e) for(int i = (s); i <= (e); ++i)#ifdef TEST    #define See(a) cout << #a << " = " << a << endl;    #define See2(a, b) cout << #a << " = " << a << ' ' << #b << " = " << b << endl;    #define debug(a, s, e) rep(_i, s, e) {cout << a[_i] << ' ';} cout << endl;    #define debug2(a, s, e, ss, ee) rep(i_, s, e) {debug(a[i_], ss, ee)}#else    #define See(a)    #define See2(a, b)    #define debug(a, s, e)    #define debug2(a, s, e, ss, ee)#endif // TESTconst int MAX = 2e9;const int MIN = -2e9;const double eps = 1e-8;const double PI = acos(-1.0);using namespace std;const int N = 100;int f[N];int a[N];double c1[N], c2[N];void init(){    f[0] = 1;    for(int i = 1; i <= 13; ++i)    {        f[i] = f[i - 1] * i;    }}int main(){    int n, m;    init();    while(~scanf("%d%d", &n, &m))    {        for(int i = 1; i <= n; ++i)        {            scanf("%d", &a[i]);        }        Mt(c1, 0);        Mt(c2, 0);        c1[0] = 1;        for(int i = 1; i <= n; ++i)        {            for(int k = 0; k <= a[i]; ++k)            {                for(int s = 0; s + k <= m; ++s)                {                    c2[s + k] += c1[s] / f[k];                }            }            for(int k = 0; k <= m; ++k)            {                c1[k] = c2[k];                c2[k] = 0;            }        }        printf("%.0f\n", c1[m] * f[m]);    }    return 0;}