杨辉三角求组合数模板

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
using namespace std;
typedef long long ll;
const int maxn = 2000+10;
const int mod = 998244353;
const int inf = 0x3f3f3f3f;
#define rep(i,first,second) for(ll i=first;i<=second;i++)
#define dep(i,first,second) for(ll i=first;i>=second;i--)
#define erep(i,u) for(ll i=head[u];~i;i=e[i].nxt)
#define lowbit(i) i&(-i)

int a[maxn][maxn];
void init(){
    rep(i,1,2000){
        a[i][0]=a[i][i]=1;
        rep(j,1,i-1){
            a[i][j]=(a[i-1][j]+a[i-1][j-1])%mod;
        }
    }
}
int main()
{
    init();
    int n,m;
    while(~scanf("%d%d",&n,&m)){
        printf("%d\n",a[n][m]);
    }
    return 0;
}