Codeforces 23E Tree

http://codeforces.com/problemset/problem/23/E

题意:给一个树，求砍断某些边，使得所有联通块大小的乘积最大。
思路:f[i][j]代表当前把j个贡献给i的父亲(也就是不计入f[i][j])的最大乘积是多少，转移就是背包转移

记得最后统计答案的时候是f[i][j]*j

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<iostream>
#define wk sb
#define ll long long
int tot,son[],first[],next[],go[];
int n;
struct node{
    int a[],n;
}f[][];
int read(){
    int t=,f=;char ch=getchar();
    while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
    while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
    return t*f;
}
void insert(int x,int y){
    tot++;
    go[tot]=y;
    next[tot]=first[x];
    first[x]=tot;
}
void add(int x,int y){
    insert(x,y);insert(y,x);
}
node operator *(node a,node b){
    node c;c.n=;for (int i=;i<=;i++) c.a[i]=;
    c.n=a.n+b.n;
    for (int i=;i<=a.n;i++)
        for (int j=;j<=b.n;j++){
            c.a[i+j-]+=a.a[i]*b.a[j];
            c.a[i+j]+=c.a[i+j-]/;
            c.a[i+j-]%=;
        }
    int j=;
    while (j<=c.n||c.a[j]>){
         c.a[j+]+=c.a[j]/;
         c.a[j]%=;
         j++;
    }
    while (j>&&c.a[j]==) j--;
    c.n=j;
    return c;
}
node make(int x){
    node c;
    c.n=;for (int i=;i<=;i++) c.a[i]=;
    while (x){
       c.a[++c.n]=x%;
       x/=;
    }
    return c;
}
node up(node a,node b){
    if (a.n>b.n) return a;
    if (b.n>a.n) return b;
    for (int i=a.n;i>=;i--)
        if (a.a[i]>b.a[i]) return a;
        else
        if (b.a[i]>a.a[i]) return b;
    return a;
}
void dfs(int x,int fa){
    f[x][]=make();
    son[x]=;
    for (int i=first[x];i;i=next[i]){
         int pur=go[i];
         if (pur==fa) continue;
         dfs(pur,x);
         for (int j=son[x];j>=;j--)
            for (int k=son[pur];k>=;k--)
                f[x][j+k]=up(f[x][j+k],f[x][j]*f[pur][k]);
         son[x]+=son[pur];
    }
    f[x][]=make();
    for (int i=;i<=son[x];i++)
        f[x][]=up(f[x][],f[x][i]*make(i));
}
int main(){
    n=read();
    for (int i=;i<n;i++){
         int x=read(),y=read();
         add(x,y);
    }
    dfs(,);
    printf("%d",(int)f[][].a[f[][].n]);
    for (int i=f[][].n-;i>=;i--)
        printf("%.4d",(int)f[][].a[i]);
}