hdu 1086 You can Solve a Geometry Problem too 线段相交

#include <iostream>#include <cstdio>using namespace std;struct node{    double xs, ys;    double xe, ye;}p[231];double Ijs(int i, double x, double y){    return (p[i].xs-x) * (p[i].ye-y) - (p[i].ys-y) * (p[i].xe-x);}bool Iseg(int i,  int j){    if(min(p[i].xs, p[i].xe) <= max(p[j].xs, p[j].xe) &&       min(p[i].ys, p[i].ye) <= max(p[j].ys, p[j].ye) &&       min(p[j].xs, p[j].xe) <= max(p[i].xs, p[i].xe) &&       min(p[j].ys, p[j].ye) <= max(p[i].ys, p[i].ye) &&       Ijs(i, p[j].xs, p[j].ys) * Ijs(i, p[j].xe, p[j].ye) <= 0 &&       Ijs(j, p[i].xs, p[i].ys) * Ijs(j, p[i].xe, p[i].ye) <= 0)        return true;    return false;}int main(){    int n;    while(scanf("%d", &n) != EOF && n)    {        for(int i = 0; i < n; i++)        scanf("%lf%lf%lf%lf", &p[i].xs, &p[i].ys, &p[i].xe, &p[i].ye);        int sum = 0;        for(int i = 0; i < n-1; i++)            for(int j = i+1; j < n; j++)            if(Iseg(i, j)) sum++;        cout << sum << endl;    }}