原题链接
代码展示
#include <iostream>
#include <vector>
using namespace std;
vector<int> add(vector<int> &A,vector<int> &B)
{
vector<int> C;
int t=0;
for(int i=0;i<A.size() || i<B.size();i++)
{
if(i<A.size()) t+=A[i];
if(i<B.size()) t+=B[i];
C.push_back(t%10);
t/=10;
}
if(t) C.push_back(1);
return C;
}
void calculateFactorial(int n, vector<int> &result) {
result.push_back(1);
for (int i = 2; i <= n; ++i) {
int carry = 0;
for (size_t j = 0; j < result.size(); ++j) {
int product = result[j] * i + carry;
result[j] = product % 10;
carry = product / 10;
}
while (carry > 0) {
result.push_back(carry % 10);
carry /= 10;
}
}
}
int main() {
int n;
cin >> n;
vector<int> sum;
for(int i=1;i<=n;i++){
vector<int> factorial;
calculateFactorial(i, factorial);
sum = add(sum, factorial);
}
for(int i=sum.size()-1;i>=0;i--){
cout << sum[i];
}
return 0;
} 第二段函数calculateFactorial是求大数阶乘。这一段实际是将上一篇文章的高精度计算融合起来得出的。
后续优化（统一，简单易懂，简洁）
#include <iostream>
#include <vector>
using namespace std;
vector<int> add(vector<int> a, vector<int> b){
vector<int> c(a.size()+b.size(),0);
int carry = 0;
for(int i = 0; i<a.size() || i<b.size(); i++){
if(i<a.size()) carry += a[i];
if(i<b.size()) carry += b[i];
c[i] = carry%10;
carry /= 10;
}
while(carry){
c.push_back(carry%10);
carry /= 10;
}
return c;
}
vector<int> facterial(int n){
vector<int> original(1,1);
for(int i = 1; i <= n; i++){
int carry = 0;
for(int j = 0; j < original.size(); j++){
int product = original[j]*i + carry;
original[j] = product%10;
carry = product/10;
}
while(carry){
original.push_back(carry%10);
carry /= 10;
}
}
return original;
}
int main(){
vector<int> sum;
const int MAX = 20;
for(int i = 1; i <= MAX; i++){
sum =add(sum,facterial(i));
}
while(sum.back() == 0 && sum.size() > 1) sum.pop_back();
for(int i = sum.size()-1; i>=0; i--){
cout<<sum[i];
}
return 0;
}