HDOJ HDU 1131 Count the Trees

HDOJ 1131 Count the Trees

题目

点此查看 HDOJ 1131 Count the Trees

题意

给 n 个元素 可得到多少种不同的 树
一下是 2 的 4 种

题解

$C_{n * 2}^{ n + 2} = {n * 2 !\over n + 2!}$

代码

#include <iostream>
#include <iomanip>
#include <cstring>

#define maxnum 100
#define maxint 10000
using namespace std;

struct bigint
{
    int m;
    int perint[maxnum];

    bigint()
    {
        for(int i = 0;i < maxnum;i++)
            perint[i] = 0;
    }
    bigint & operator*(int b)
    {
        int c = 0,cur;
        for(int i = 0;i <= m;i++)
        {
            cur = perint[i] * b + c;
            perint[i] = cur % maxint;
            c = cur / maxint;
        }
        if(c)
        {
            m++;
            perint[m] = c;
        }
        return *this;
    }
    friend ostream & operator<<(ostream &out,bigint & b)
    {
        out << b.perint[b.m];
        for(int i = b.m - 1;i >= 0;i--)
                out << setw(4) << setfill('0') << b.perint[i];
        return out;
    }
};

int main()
{
    int nm;
    bigint t;
    while(cin >> nm && nm)
    {
        t.perint[0] = 1;
        t.m = 0;
        for(int i = nm + 2;i <= nm * 2;i++)
            t * i;
        cout << t << endl;
        memset(t.perint,0,sizeof(t.perint));
    }
    return 0;
}