usaco2.1usaco_Ordered Fractions

/*ID:usaco100LANG:C++TASK:frac1*/#include<stdio.h>#include<iostream>#include<cmath>#include<algorithm>using namespace std;struct node{    int up,down;}A[25600];int n,top;void swap(int &x,int &y){     int tmp=x;     x=y;     y=tmp;}int gcd(int x,int y){    if (x>y) swap(x,y);    if (x==0) return y;    return (gcd(y%x,x));}void  init(){     top=0;  for(int  i=1;i<=n;i++)    for(int  j=0;j<=i;j++)    {      int  a=j,b=i;      if(gcd(a,b)==1)      {A[top].up=a;A[top].down=b;top++;      }    }}int cmp(node x,node y){    return (double)x.up/x.down<(double)y.up/y.down;}int main(){    freopen("frac1.in","r",stdin);    freopen("frac1.out","w",stdout);    cin>>n;    init();    sort(A,A+top,cmp);    for(int i=0;i<top;i++)        printf("%d/%d\n",A[i].up,A[i].down);    return 0;}