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小a的学期

https://blog.csdn.net/u011815404/article/details/88381586

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#include<iostream>
#include<vector>
#include <cstring> 
#include<string>
using namespace std;
struct wint:vector<int>
{
    wint(int n=0)
    {
        push_back(n);
        check();
    }
    wint& check()//
    {
        while(!empty()&&!back())pop_back();
        if(empty())return *this;
        for(int i=1; i<size(); ++i)
        {
            (*this)[i]+=(*this)[i-1]/10;
            (*this)[i-1]%=10;
        }
        while(back()>=10)
        {
            push_back(back()/10);
            (*this)[size()-2]%=10;
        }
        return *this;//
    }
};
 
istream& operator>>(istream &is,wint &n)
{
    string s;
    is>>s;
    n.clear();
    for(int i=s.size()-1; i>=0; --i)n.push_back(s[i]-'0');
    return is;
}
ostream& operator<<(ostream &os,const wint &n)
{
    if(n.empty())os<<0;
    for(int i=n.size()-1; i>=0; --i)os<<n[i];
    return os;
}
 
bool operator!=(const wint &a,const wint &b)
{
    if(a.size()!=b.size())return 1;
    for(int i=a.size()-1; i>=0; --i)
        if(a[i]!=b[i])return 1;
    return 0;
}
bool operator==(const wint &a,const wint &b)
{
    return !(a!=b);
}
bool operator<(const wint &a,const wint &b)
{
    if(a.size()!=b.size())return a.size()<b.size();
    for(int i=a.size()-1; i>=0; --i)
        if(a[i]!=b[i])return a[i]<b[i];
    return 0;
}
bool operator>(const wint &a,const wint &b)
{
    return b<a;
}
bool operator<=(const wint &a,const wint &b)
{
    return !(a>b);
}
bool operator>=(const wint &a,const wint &b)
{
    return !(a<b);
}
 
wint& operator+=(wint &a,const wint &b)
{
    if(a.size()<b.size())a.resize(b.size());
    for(int i=0; i!=b.size(); ++i)a[i]+=b[i];
    return a.check();
}
wint operator+(wint a,const wint &b)
{
    return a+=b;
}
 
wint& operator-=(wint &a,wint b)
{
    if(a<b)swap(a,b);
    for(int i=0; i!=b.size(); a[i]-=b[i],++i)
        if(a[i]<b[i])//需要借位
        {
            int j=i+1;
            while(!a[j])++j;
            while(j>i)
            {
                --a[j];
                a[--j]+=10;
            }
        }
    return a.check();
}
wint operator-(wint a,const wint &b)
{
    return a-=b;
}
 
wint operator*(const wint &a,const wint &b)
{
    wint n;
    n.assign(a.size()+b.size()-1,0);
    for(int i=0; i!=a.size(); ++i)
        for(int j=0; j!=b.size(); ++j)
            n[i+j]+=a[i]*b[j];
    return n.check();
}
wint& operator*=(wint &a,const wint &b)
{
    return a=a*b;
}
 
wint divmod(wint &a,const wint &b)
{
    wint ans;
    for(int t=a.size()-b.size(); a>=b; --t)
    {
        wint d;
        d.assign(t+1,0);
        d.back()=1;
        wint c=b*d;
        while(a>=c)
        {
            a-=c;
            ans+=d;
        }
    }
    return ans;
}
wint operator/(wint a,const wint &b)
{
    return divmod(a,b);
}
wint& operator/=(wint &a,const wint &b)
{
    return a=a/b;
}
wint& operator%=(wint &a,const wint &b)
{
    divmod(a,b);
    return a;
}
wint operator%(wint a,const wint &b)
{
    return a%=b;
}
 
wint pow(const wint &n,const wint &k)
{
    if(k.empty())return 1;
    if(k==2)return n*n;
    if(k.front()%2)return n*pow(n,k-1);
    return pow(pow(n,k/2),2);
}
 
 
wint c[102][102] ;
 
void init(){
    c[1][1]=1; 
    for(int i=0;i<=100;++i) c[i][0] = 1;
    for(int i=2;i<=100;++i)
     for(int j=1;j<=100;++j)
        c[i][j] =c[i-1][j]+c[i-1][j-1] ;
}
wint C(int n,int m,wint p){
    return c[n][m]%p ;
}
 
int main(){
    init() ;
    int n,m;
    wint p;
    cin>>n>>m>>p ;
     
    wint res1=C(2*n,n,p);
    wint res2=0;
    if(m<=n)
        res2=C(2*n,n+m,p);
  
    wint res=(((res1-res2)%p)+p)%p;
    cout << res<<'\n';
  
    return 0;
}