阶乘最后非零位
1 #include<string.h> 2 #define MAXN 10000 3 int lastdigit(char*buf) 4 { 5 const int mod[20] = {1,1,2,6,4,2,2,4,2,8,4,4,8,4,6,8,8,6,8,2}; 6 int len = strlen(buf),a[MAXN],i,c,ret = 1; 7 if(len == 1) 8 return mod[buf[0]-'0']; 9 for(i = 0;i<len;i++) 10 a[i] = buf[len-1-i]-'0'; 11 for(;len;len-=!a[len-1]) 12 { 13 ret = ret*mod[a[1]%2*10+a[0]]%5; 14 for(c = 0,i = len-1;i>=0;i--){ 15 c = c*10+a[i]; 16 a[i] = c/5; 17 c%=5; 18 } 19 } 20 return ret+ret%2*5; 21 }
