poj1127

floyd+几何计算

线段相交

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define maxn 20
#define zero(x) (((x)>0?(x):-(x))<eps)
#define eps 1.0E-8

struct Point
{
    double x, y;
};

struct Line
{
    Point a, b;
} straw[maxn];

bool g[maxn][maxn];
int n;

void input()
{
    for (int i = 0; i < n; i++)
        scanf("%lf%lf%lf%lf", &straw[i].a.x, &straw[i].a.y, &straw[i].b.x, &straw[i].b.y);
}

double xmult(Point p1, Point p2, Point p0)
{
    return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}

int dots_inline(Point p1, Point p2, Point p3)
{
    return zero(xmult(p1, p2, p3));
}

int same_side(Point p1, Point p2, Line l)
{
    return xmult(l.a, p1, l.b) * xmult(l.a, p2, l.b) > eps;
}

int dot_online_in(Point p, Line l)
{
    return zero(xmult(p, l.a, l.b)) && (l.a.x - p.x) * (l.b.x - p.x) < eps && (l.a.y - p.y) * (l.b.y - p.y) < eps;
}

int intersect_in(Line u, Line v)
{
    if (!dots_inline(u.a, u.b, v.a) || !dots_inline(u.a, u.b, v.b))
        return !same_side(u.a, u.b, v) && !same_side(v.a, v.b, u);
    return dot_online_in(u.a, v) || dot_online_in(u.b, v) || dot_online_in(v.a, u) || dot_online_in(v.b, u);
}

void make()
{
    for (int i = 0; i < n; i++)
        g[i][i] = true;
    for (int i = 0; i < n - 1; i++)
        for (int j = i + 1; j < n; j++)
            if (intersect_in(straw[i], straw[j]))
                g[i][j] = g[j][i] = true;
}

void floyd()
{
    for (int k = 0; k < n; k++)
        for (int i = 0; i < n; i++)
            for (int j = 0; j < n; j++)
                if (g[i][k] && g[k][j])
                    g[i][j] = true;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%d", &n), n)
    {
        memset(g, 0, sizeof(g));
        input();
        make();
        floyd();
        int a, b;
        while (scanf("%d%d", &a, &b), a | b)
        {
            a--;
            b--;
            if (g[a][b])
                printf("CONNECTED\n");
            else
                printf("NOT CONNECTED\n");
        }
    }
    return 0;
}