【HDOJ】1466 计算直线的交点数

找了个规律。

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #define MAXN 21

 int buf[MAXN][];
 int lens[MAXN];

 int comp(const void *a, const void *b) {
     return *(int *)a - *(int *)b;
 }

 int main() {
     int i, j, k, tmp, p, flg;
     memset(lens, , sizeof(lens));
     memset(buf, , sizeof(buf));
     lens[] = ;
     lens[] = ;
     lens[] = ;
     buf[][] = ;

     for (i=; i<MAXN; ++i) {
         lens[i] = ;
         for (j=; j<i; ++j) {
             for (k=; k<lens[j]; ++k) {
                 tmp = (i-j)*j+buf[j][k];
                 flg = ;
                 for (p=lens[i]-; p>=; --p) {
                     if (buf[i][p] == tmp) {
                         flg = ;
                         break;
                     }
                 }
                 if (flg)
                     buf[i][lens[i]++] = tmp;
             }
         }
         qsort(buf[i], lens[i], sizeof(int), comp);
     }

     while (scanf("%d", &k) != EOF) {
         printf("%d", buf[k][]);
         for (i=; i<lens[k]; ++i) {
             if (buf[k][i] != buf[k][i-])
                 printf(" %d", buf[k][i]);
         }
         printf("\n");
     }

     return ;
 }