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。

View Code
#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;
}

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