SGU 106 解题手记
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#include <iostream>
#include <cmath>
using namespace std;
 
int extended_euclid(int a,int b,int &x,int &y)
{
    if (b)
    {
        int r=extended_euclid(b,a%b,x,y);
        int t=y;
        y=x-(a/b)*y;
        x=t;
        return r;
    }
    else
    {
        x=1; y=0;
        return a;
    }
}
 
int main()
{
    int oa,ob,a,b,c,x1,x2,y1,y2,x0,y0;
    cin>>a>>b>>c>>x1>>x2>>y1>>y2; c=-c; oa=a; ob=b;
    if (x1>x2 || y1>y2)
    {
        cout<<0; return 0;
    }
    if (a==0 && b==0)
    {
        if (c==0) cout<<static_cast<long long>(x2-x1+1)*(y2-y1+1);
        else cout<<0;
        return 0;
    }
    if (a==0)
    {
        if (c%b==0 && y1<=c/b && c/b<=y2) cout<<1;
        else cout<<0;
        return 0;
    }
    if (b==0)
    {
        if (c%a==0 && x1<=c/a && c/a<=x2) cout<<1;
        else cout<<0;
        return 0;
    }
    int transx=(a>0?1:-1),transy=(b>0?1:-1);
    if (c<0)
    {
        transx=-transx; transy=-transy;
    }
    a=abs(a); b=abs(b); c=abs(c);
    int d=extended_euclid(a,b,x0,y0);
    if (c%d)
    {
        cout<<0; return 0;
    }
    x0*=c/d; y0=(c-static_cast<long long>(a)*x0)/b;
    x0*=transx; y0*=transy;
    a=oa/d; b=ob/d;
    if (a<0) swap(y1,y2);
    if (b<0) swap(x1,x2);
    int mini=max(ceil(static_cast<double>(x1-x0)/b),ceil(static_cast<double>(y0-y2)/a));
    int maxi=min(floor(static_cast<double>(x2-x0)/b),floor(static_cast<double>(y0-y1)/a));
    if (maxi>=mini) cout<<maxi-mini+1;
    else cout<<0;
    return 0;
}