hdu 1294 Rooted Trees Problem 组合数+整数划分

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#include <cstdio>#include <cstring>#include <cmath>#include <iostream>#include <algorithm>using namespace std;#define LL __int64const LL maxn=44;LL dp[maxn]={0,1,1,2,4,9,20,48,115,286,719,1842,4766,12486,32973,87811,235381,634847,1721159,4688676,                12826228,35221832,97055181,268282855,743724984,2067174645,5759636510,16083734329,                45007066269,126186554308,354426847597,997171512998,2809934352700,7929819784355,                22409533673568,63411730258053,179655930440464,509588049810620,1447023384581029,                4113254119923150,11703780079612453};//可以直接打表了。。LL e[maxn],t,s;LL C(LL n,LL m)//求组合数{    m=min(m,n-m);    LL i,s=1;    for(i=1;i<=m;i++)        s=s*(n-i+1)/i;    return s;}void dfs(LL a,LL step,LL num,LL sum){    LL i,j,k;    if(sum>num)return;    if(sum==num)    {        LL s=1;        k=1;        for(i=1;i<step;i++)        {            if(e[i]!=e[i-1])            {                s*=C(dp[e[i-1]]+k-1,k);                k=0;            }            k++;        }        s*=C(dp[e[step-1]]+k-1,k);        dp[num+1]+=s;        return;    }    for(i=a;i<=num;i++)    {        e[step]=i;        dfs(i,step+1,num,sum+i);    }}void init(){    dp[1]=dp[2]=1;    LL i,j,k;    for(i=3;i<=40;i++)    {        dp[i]=0;        dfs(1,0,i-1,0);    }}int main(){    init();    LL n;    while(cin>>n)    {        cout<<dp[n]<<endl;    }    return 0;}/*    可重复选择的组合。有n个元素,每个元素可以选多次,一共选k个袁术,有多少种选择?    n=3,k=2,有6种:(1,1),(1,2),(1,3),(2,2),(2,3),(3,3)    共 C(k+n-1,n-1)=C(n+k-1,k)种    本题,求n个结点数的树有多少种,可采用整数划分n-1的方法    n=5时,划分4=1+1+1+1=1+1+2=1+3=2+2=4。    则dp[5]=C(dp[1]+4-1,4)+C(dp[1]+2-1,2)*dp[2]+dp[1]*dp[3]+dp[2]*dp[2]+dp[4]=9;*/

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