USACO sec2.1 Ordered Fractions

首先两重 for 循环对可能取的值约分，分子分母分别存放，根据比较分数大小的方法排序，然后按顺序输出（相同的只输出一个）；

/*

PROG : frac1

LANG : C++

*/

# include <stdio.h>

# include <stdlib.h>



# define MAXN (160 * 160)



/***************************************************/

int num[MAXN], den[MAXN], r[MAXN], m = 0;

int cmp(const void *xx, const void *yy)

{

    int x = *(int*)xx;

    int y = *(int*)yy;

    return num[x]*den[y] > den[x]*num[y] ? 1 : -1;

}



int gcd(int a, int b)

{

    if (!b) return a;

    return gcd(b, a%b);

}



void solve(void)

{

    int i, j, n;

    scanf("%d", &n);

    num[0] = 0, den[0] = 1;

    for (i = 1; i <= n; ++i)

    for (j = 1; j <= n; ++j)

    {

        if (i > j) continue;

        ++m;

        num[m] = i/gcd(i, j);

        den[m] = j/gcd(i, j);

    }

    for (i = 0; i <= m; ++i) r[i] = i;

    qsort(r, m, sizeof(r[0]), cmp);

    printf("%d/%d\n", num[r[0]], den[r[0]]);

    for (i = 1; i <= m; ++i)

    {

        if (num[r[i]] == num[r[i-1]] && den[r[i]] == den[r[i-1]])

            continue;

        else

            printf("%d/%d\n", num[r[i]], den[r[i]]);

    }

}



/***************************************************/



int main()

{

    freopen("frac1.in", "r", stdin);

    freopen("frac1.out", "w", stdout);

    

    solve();

    

    fclose(stdin);

    fclose(stdout);

    

    return 0;

}