FZU2278（大数）

题解:就是让你求n!(1+1/2+1/3+..1/n)，大数模拟一下就好了

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
typedef long long int ll;
const ll mod = 1e4;
ll now[6000],sum[6000],ans[6000];
int len1,len2,len3;
ll c;
void calc(int x){
int i;
for(c=0,i=0; i<=len1;i++){
long p= now[i]*x+c;
now[i]= p % 10000;
c=p / 10000;
}
now[i]= c;
if (c>0)
len1++;
}
void det(int x){
c = 0;
for(int i = len1; i >= 0; i--){
sum[i] = (now[i]+c)/x;
// cout<<sum[i]<<endl;
c = (now[i]+c)%x;
c *= mod;
}
}
void add(){
for(int i = 0; i <= len1; i++)
ans[i] += sum[i];
for(int i = 0; i <= len3; i++)
ans[i+1]+=ans[i]/mod,ans[i]%=mod;
if(ans[len3+1]>0)
len3++;
}
int main(){
int t,n;
scanf("%d",&t);
while(t--){
scanf("%d",&n);
memset(ans,0,sizeof(ans));
memset(now,0,sizeof(now));
now[0] = 1;
len1 = 0;
len2 = 0;
len3 = 0;
for(int i = 1; i <= n; i++)
calc(i);
//for(int i = len1; i >= 0; i--)
// printf("%04d",now[i]);
//puts("");
len3 = len1;
// cout<<len1<<endl;
for(int i = 1; i <= n; i++){
det(i);
add();
}
printf("%I64d",ans[len3]);
for(int i = len3-1; i >= 0; i--)
printf("%04I64d",ans[i]);
printf(".0\n");
}
return 0;
}