【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][150];
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, 0, sizeof(lens));
    memset(buf, 0, sizeof(buf));
    lens[0] = 1;
    lens[1] = 1;
    lens[2] = 2;
    buf[2][1] = 1;

    for (i=3; i<MAXN; ++i) {
        lens[i] = 1;
        for (j=1; j<i; ++j) {
            for (k=0; k<lens[j]; ++k) {
                tmp = (i-j)*j+buf[j][k];
                flg = 1;
                for (p=lens[i]-1; p>=0; --p) {
                    if (buf[i][p] == tmp) {
                        flg = 0;
                        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][0]);
        for (i=1; i<lens[k]; ++i) {
            if (buf[k][i] != buf[k][i-1])
                printf(" %d", buf[k][i]);
        }
        printf("
");
    }

    return 0;
}