src2020/1805_kclimb/kclimb.cpp

#include<iostream>
using namespace std;
int main(){
    int n,k,f[21][21]={1};
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=i;j++){
            f[i][j]=f[i-1][j]+f[i-1][j-1]*j;
            if(j==k) break;
        }
    }
    cout<<f[n][k];
}