poj1410

计算几何

题意：问线段与矩形（边与坐标轴平行）是否相交

分析：分别判断4条边与线段是否相交，在判断线段两端点是否在矩形内。

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

#define eps 1E-10

struct Point
{
    int x, y;
} point[5], s, e;

bool in(Point &a)
{
    if (a.x <= point[2].x && a.x >= point[0].x && a.y <= point[2].y && a.y
            >= point[0].y)
        return true;
    return false;
}

bool inter(Point &a, Point &b, Point &c, Point &d)
{
    if (min(a.x, b.x) > max(c.x, d.x) || min(a.y, b.y) > max(c.y, d.y) || min(
            c.x, d.x) > max(a.x, b.x) || min(c.y, d.y) > max(a.y, b.y))
        return 0;
    double h, i, j, k;
    h = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
    i = (b.x - a.x) * (d.y - a.y) - (b.y - a.y) * (d.x - a.x);
    j = (d.x - c.x) * (a.y - c.y) - (d.y - c.y) * (a.x - c.x);
    k = (d.x - c.x) * (b.y - c.y) - (d.y - c.y) * (b.x - c.x);
    return h * i <= eps && j * k <= eps;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    int t;
    scanf("%d", &t);
    while (t--)
    {
        scanf("%d%d%d%d%d%d%d%d", &s.x, &s.y, &e.x, &e.y, &point[0].x,
                &point[0].y, &point[2].x, &point[2].y);
        if (point[0].x > point[2].x)
            swap(point[0].x, point[2].x);
        if (point[0].y > point[2].y)
            swap(point[0].y, point[2].y);
        point[1].x = point[0].x;
        point[1].y = point[2].y;
        point[3].x = point[2].x;
        point[3].y = point[0].y;
        point[4] = point[0];
        bool ok = false;
        for (int i = 0; i < 4; i++)
            if (inter(point[i], point[i + 1], s, e))
            {
                ok = true;
                break;
            }
        if (in(s) || in(e))
            ok = true;
        if (ok)
            printf("T\n");
        else
            printf("F\n");
    }
    return 0;
}