标签：pre time 阶乘 std factor 数字 const 求和 print
题目要求：输入n，计算s = 1！+2！+3！+…n！的末6位，n<=10^6
样例输入：10
样例输出：37913
源代码：
1 #include <stdio.h> 2 #include <time.h> 3 4 int main() 5 { 6 //const int MOD = 1000000; 7 int i,j,n,s = 0; 8 scanf("%d",&n); 9 for (i = 1;i <= n;i++) 10 { 11 int factorial = 1; 12 for (j = 1;j <= i;j++) 13 factorial = (factorial * j ); 14 s = (s + factorial); 15 } 16 printf("%d\n",s%1000000); 17 printf("Time = %.21f\n",(double)clock() / CLOCKS_PER_SEC); 18 return 0; 19 }
这是先求和再取模
如果逐步取模再求和的话，如下：
1 #include <stdio.h> 2 #include <time.h> 3 4 int main() 5 { 6 const int MOD = 1000000; 7 int i,j,n,s = 0; 8 scanf("%d",&n); 9 for (i = 1;i <= n;i++) 10 { 11 int factorial = 1; 12 for (j = 1;j <= i;j++) 13 factorial = (factorial * j %MOD); 14 s = (s + factorial)%MOD; 15 } 16 printf("%d\n",s); 17 printf("Time = %.21f\n",(double)clock() / CLOCKS_PER_SEC); 18 return 0; 19 }
第一段的话，小数字可以，输入100就乘法溢出了
第二段大数字也可以，就是数字过大程序跑得时间太长了；
标签：pre time 阶乘 std factor 数字 const 求和 print
原文地址：http://www.cnblogs.com/zhangzemin/p/6012960.html
