! means n × (n − 1) × ... × 3 × 2 × 1
For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
Find the sum of the digits in the number 100!
n!表示n ×(n -1)×...×3×2×1
例如,10!= 10×9×...×3×2×1 = 3628800,数字10的位数之和是3 + 6 + 2 + 8 + 8 + 0 + 0 = 27。
找到数字100中的位数数字之和!
思路
大整数相乘(与第十六题一样)
#include <stdio.h>
int mul[500] = {0};
int main(){
mul[0] = mul[1] = 1;
for(int i = 2; i < 100; i++){
for(int j = 1; j <= mul[0]; j++){
mul[j] *= i;
}
for(int j = 1; j <= mul[0]; j++){
if(mul[j] < 10) continue;
mul[j + 1] += mul[j] / 10;
mul[j] %= 10;
mul[0] += (mul[0] == j);
}
}
int sum = 0;
for(int i = 1; i <= mul[0]; i++){
sum += mul[i];
}
printf("%d\n",sum);
return 0;
}