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;elseprintf("%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;
}