【HDOJ】1099 Lottery

题意超难懂，实则一道概率论的题目。求P(n)。
P(n) = n*(1+1/2+1/3+1/4+...+1/n)。
结果如果可以除尽则表示为整数，否则表示为假分数。

 #include <cstdio>
 #include <cstring>

 #define MAXN 25

 __int64 buf[MAXN];

 __int64 gcd(__int64 a, __int64 b) {
     if (b == ) return a;
     else    return gcd(b, a%b);
 }

 int main() {
     int i, j, k, n;
     __int64 fz, fm, tmp, intr;

     buf[] = ;
     for (i=; i<=; ++i)
         buf[i] = i*buf[i-]/gcd(i, buf[i-]);

     while (scanf("%d", &n) != EOF) {
         fz = ;
         fm = buf[n];
         for (i=; i<=n; ++i)
             fz += fm/i;
         fz *= n;
         tmp = gcd(fz, fm);
         fz /= tmp;
         fm /= tmp;
         tmp = fz/fm;
         fz -= tmp*fm;
         if (fz == ) {
             printf("%I64d\n", tmp);
             continue;
         }
         n = ;
         intr = tmp;
         while (tmp) {
             ++n;
             tmp /= ;
         }
         for (i=; i<=n; ++i)
             printf(" ");
         printf("%I64d\n", fz);
         printf("%I64d ", intr);
         j = k = ;
         while (fz) {
             ++j;
             fz /= ;
         }
         tmp = fm;
         while (tmp) {
             ++k;
             tmp /= ;
         }
         j = (j>k) ? j:k;
         for (i=; i<j; ++i)
             printf("-");
         printf("\n");
         for (i=; i<=n; ++i)
             printf(" ");
         printf("%I64d\n", fm);
     }

     return ;
 }