POJ 1410 Intersection 判斷線段交和點在矩形內 【計算幾何】
Intersection
| Time Limit: 1000MS | Memory Limit: 10000K |
| Total Submissions: 9996 | Accepted: 2632 |
Description
You are to write a program that has to decide whether a given line segment intersects a given rectangle.
An example:
line: start point: (4,9)
end point: (11,2)
rectangle: left-top: (1,5)
right-bottom: (7,1) 
Input
The input consists of n test cases. The first line of the input file contains the number n. Each following line contains one test case of the format: xstart ystart xend yend xleft ytop xright ybottom where (xstart, ystart) is the start and (xend, yend) the end point of the line and (xleft, ytop) the top left and (xright, ybottom) the bottom right corner of the rectangle. The eight numbers are separated by a blank. The terms top left and bottom right do not imply any ordering of coordinates.
Output
For each test case in the input file, the output file should contain a line consisting either of the letter "T" if the line segment intersects the rectangle or the letter "F" if the line segment does not intersect the rectangle.
Sample Input
1 4 9 11 2 1 5 7 1
Sample Output
F
Source
題意：
給了一個線段和矩形。如果線段和矩形的邊相交，或者線段在矩形內。輸出T，否則輸出F
思路：
先判斷矩形4條邊是否與線段相交，然後判斷線段兩個端點是否在矩形內
//判斷線段相交和點在矩形內
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <queue>
#include <map>
#include <vector>
#include <set>
#include <string>
#include <math.h>
using namespace std;
const double eps = 1e-8;
int sgn(double x)
{
if(fabs(x) < eps)return 0;
if(x < 0)return -1;
else return 1;
}
struct Point
{
double x,y;
Point(){}
Point(double _x,double _y)
{
x = _x;y = _y;
}
Point operator -(const Point &b)const
{
return Point(x - b.x,y - b.y);
}
//叉積
double operator ^(const Point &b)const
{
return x*b.y - y*b.x;
}
//點積
double operator *(const Point &b)const
{
return x*b.x + y*b.y;
}
//繞原點旋轉角度B（弧度值），後x,y的變化
void transXY(double B)
{
double tx = x,ty = y;
x = tx*cos(B) - ty*sin(B);
y = tx*sin(B) + ty*cos(B);
}
};
struct Line
{
Point s,e;
double k;
Line(){}
Line(Point _s,Point _e)
{
s = _s;e = _e;
k = atan2(e.y - s.y,e.x - s.x);
}
//兩條直線求交點，
//第一個值為0表示直線重合，為1表示平行，為2是相交
//只有第一個值為2時，交點才有意義
pair<int,Point> operator &(const Line &b)const
{
Point res = s;
if(sgn((s-e)^(b.s-b.e)) == 0)
{
if(sgn((s-b.e)^(b.s-b.e)) == 0)
return make_pair(0,res);//重合
else return make_pair(1,res);//平行
}
double t = ((s-b.s)^(b.s-b.e))/((s-e)^(b.s-b.e));
res.x += (e.x-s.x)*t;
res.y += (e.y-s.y)*t;
return make_pair(2,res);
}
};
//兩點間距離
double dist(Point a,Point b)
{
return sqrt((a-b)*(a-b));
}
//判斷線段相交
bool inter(Line l1,Line l2)
{
return
max(l1.s.x,l1.e.x) >= min(l2.s.x,l2.e.x) &&
max(l2.s.x,l2.e.x) >= min(l1.s.x,l1.e.x) &&
max(l1.s.y,l1.e.y) >= min(l2.s.y,l2.e.y) &&
max(l2.s.y,l2.e.y) >= min(l1.s.y,l1.e.y) &&
sgn((l2.s-l1.s)^(l1.e-l1.s))*sgn((l2.e-l1.s)^(l1.e-l1.s)) <= 0 &&
sgn((l1.s-l2.s)^(l2.e-l1.s))*sgn((l1.e-l2.s)^(l2.e-l2.s)) <= 0;
}
//判斷點線上段上
bool OnSeg(Point p,Line L)
{
return
sgn((L.s-p)^(L.e-p))==0&&
sgn((p.x-L.s.x)*(p.x-L.e.x))<=0&&
sgn((p.y-L.s.y)*(p.y-L.e.y))<=0;
}
//判斷點在凸多邊形內，點形成一個凸包，而且按逆時針排序
//如果是順時針，就把<0改成>0
//點的編號：0~n-1
//返回值：-1點在凸多邊形外，0點在凸多邊形邊上，1點在凸多邊形內
int inConvexPoly(Point a,Point p[],int n)
{
for(int i=0;i<n;i++)
{
if(sgn((p[i]-a)^(p[(i+1)%n]-a))<0)
return -1;
else if(OnSeg(a,Line(p[i],p[(i+1)%n])))
return 0;
}
return 1;
}
//判斷點在任意多邊形內
//射線法，poly[]的頂點數要大於等於3，點的編號：0~n-1
//返回值
//-1：點在多邊形外
//0：點在多邊形邊界上
//1：點在多邊形內
int inPoly(Point p,Point poly[],int n)
{
int cnt=0;
Line ray,side;
ray.s=p;
ray.s.y=p.y;
ray.e.x=-100000000000.0;//-INF,注意取值，防止越界
for(int i=0;i<n;i++)
{
side.s=poly[i];
side.e=poly[(i+1)%n];
if(OnSeg(p,side)) return 0;
//如果平行軸，則不考慮
if(sgn(side.s.y-side.e.y)==0)
continue;
if(OnSeg(side.s,ray)){
if(sgn(side.s.y-side.e.y)>0)
cnt++;
}
else if(OnSeg(side.e,ray)){
if(sgn(side.e.y-side.s.y)>0)
cnt++;
}
else if(inter(ray,side))
cnt++;
}
if(cnt%2==1)
return 1;
else
return -1;
}
int main()
{
int T;
scanf("%d",&T);
while(T--){
Line line;
scanf("%lf%lf%lf%lf",&line.s.x,&line.s.y,&line.e.x,&line.e.y);
double x1,y1,x2,y2;
scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
if(x1>x2) swap(x1,x2);
if(y1>y2) swap(y1,y2);
Point p[5];//0~3
p[0]=Point(x1,y1);//left_bottom
p[1]=Point(x2,y1);//right_bottom
p[2]=Point(x2,y2);//right_top
p[3]=Point(x1,y2);//left_top
Line bottom=Line(p[1],p[0]);
if(inter(line,bottom)){
printf("T\n");
continue;
}
Line right=Line(p[2],p[1]);
if(inter(line,right)){
printf("T\n");
continue;
}
Line top=Line(p[3],p[2]);
if(inter(line,top)){
printf("T\n");
continue;
}
Line left=Line(p[3],p[0]);
if(inter(line,left)){
printf("T\n");
continue;
}
if(inConvexPoly(line.s,p,4)>=0||inConvexPoly(line.e,p,4)>=0){
printf("T\n");
continue;
}
printf("F\n");
continue;
}
return 0;
}