[Project Euler] Problem 20

n! means n (n 1) ... 3 2 1

Find the sum of the digits in the number 100!

这道题的做法和那个求2的1000次方的各位和的思路一样

我们只需要在那道题程序的基础上稍加改变就可以了

#include < iostream >
using namespace std;

int main(){
int sum[ 200 ] = { 1 };
int tmp;
int all = 0 ;
for ( int i = 1 ;i <= 100 ;i ++ ){
int carry = 0 ;
for ( int j = 0 ;j < 200 ;j ++ ){
tmp = sum[j] * i;
sum[j] = (tmp + carry) % 10 ;
carry = (tmp + carry) / 10 ;
}
}
for ( int j = 0 ;j < 200 ;j ++ ){
all += sum[j];
}
cout << all << endl;
return 0 ;
}