【HDU 5810多校】Balls and Boxes（打表/数学）

#include <iostream>
#include <cstdio>
#define ll long long
#define N 100005
using namespace std;
ll n,m,b[N],ans,num;
ll sqr(ll x)
{
    return x*x;
}
void dfs(ll r){
    if(r==0){
        num++;
        for(int i=1;i<=m;i++)
            ans+=sqr(b[i]);
        return;
    }
    for(int i=1;i<=m;i++)
    {
        b[i]++;
        dfs(r-1);
        b[i]--;
    }    
}
int main() {
    while(~scanf("%lld%lld",&n,&m)){
        for(ll r=1;r<=n;r++){
            ans=num=0;
            dfs(r);
            ans=m*ans-r*r*num;
            num=m*m*num;
            ll g=__gcd(ans,num);
            printf("r=%lld: %lld/%lld\n",r,ans/g,num/g);
        }
    }
}

#include <algorithm>
#include <cstdio>
#define ll long long
using namespace std;
ll n,m;
int main() {
    while(scanf("%lld%lld",&n,&m),n){
        ll a=n*(m-1),b=m*m;
        ll g=__gcd(a,b);
            printf("%lld/%lld\n",a/g,b/g);
    }
}