HDU 1086 You can Solve a Geometry Problem too 两线段相交模板

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <queue>
#include <cmath>
#include <algorithm>

using namespace std;

struct L
{
    double x1,x2,y1,y2;
};

bool JudgeIntersetSegment(L l1,L l2)
{
    if(l1.x1 == l2.x1 && l1.y1 == l2.y1)
        return true;

    if(l1.x2 == l2.x2 && l1.y2 == l2.y2)
        return true;

    if(l1.x1 == l2.x2 && l1.y1 == l2.y2)
        return true;

    if(l1.x2 == l2.x1 && l1.y2 == l2.y1)
        return true;

    bool m1 = false, m2 = false;
    double x1,x2,y1,y2;

    L temp;

    x1 = l1.x1 - l2.x1;
    y1 = l1.y1 - l2.y1;

    x2 = l2.x2 - l2.x1;
    y2 = l2.y2 - l2.y1;

    if(x1*y2 - y1*x2 >= 0)
        m1 = true;

    x1 = l1.x2 - l2.x1;
    y1 = l1.y2 - l2.y1;

    if(x1*y2 - y1*x2 >= 0)
        m2 = true;

    if(m1 == m2)
        return false;

    temp = l1;
    l1 = l2;
    l2 = temp;

    x1 = l1.x1 - l2.x1;
    y1 = l1.y1 - l2.y1;

    x2 = l2.x2 - l2.x1;
    y2 = l2.y2 - l2.y1;

    m1 = false,m2 = false;

    if(x1*y2 - y1*x2 >= 0)
        m1 = true;

    x1 = l1.x2 - l2.x1;
    y1 = l1.y2 - l2.y1;

    if(x1*y2 - y1*x2 >= 0)
        m2 = true;

    if(m1 == m2)
        return false;
    return true;
}

int main()
{
    int countis, i,j,n;

    L line[110];

    while(scanf("%d",&n) && n)
    {
        countis = 0;
        for(i = 0;i < n; ++i)
        {
            cin>>line[i].x1>>line[i].y1>>line[i].x2>>line[i].y2;
        }

        for(i = 0;i < n; ++i)
        {
            for(j = i+1;j < n; ++j)
            {
                if(JudgeIntersetSegment(line[i],line[j]))
                    ++countis;
            }
        }
        cout<<countis<<endl;
    }
    return 0;
}