【洛谷P2822 组合数问题】

题目连接

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cctype>
#define ll long long
#define gc() getchar()
#define maxn 2005
using namespace std;
inline ll read()
{
    ll a=;int f=;char p=gc();
    while(!isdigit(p)){f|=p=='-';p=gc();}
    while(isdigit(p)){a=(a<<)+(a<<)+(p^);p=gc();}
    return f?-a:a;
}
void write(ll a)
{
    if(a>)write(a/);
    putchar(a%+'');
}

int t,k,c[maxn][maxn],f[maxn][maxn];
int main()
{
    t=read();k=read();
    for(int i=;i<=;++i)c[i][]=;
    for(int i=;i<=;++i)
        for(int j=;j<=i;++j)
            c[i][j]=(c[i-][j-]+c[i-][j])%k;
    for(int i=;i<=;++i)
    {
        for(int j=;j<=i;++j)
        {
            f[i][j]=f[i-][j]+f[i][j-]-f[i-][j-];
            if(!c[i][j])f[i][j]++;
        }
        f[i][i+]=f[i][i];
    }
    for(int i=;i<=t;++i)
    {
        int n=read(),m=read();
        if(m>n)m=n;
        write(f[n][m]);
        putchar('\n');
    }
    return ;
}

by子谦。（是HMY，不是钟子谦奆佬QWQ）大佬的面对面讲解