poj 1127 判断任意两线段是否相交，叉积+floyd（并查集）@

Jack Straws

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 4342		Accepted: 1976

Description

In the game of Jack Straws, a number of plastic or wooden "straws" are dumped on the table and players try to remove them one-by-one without disturbing the other straws. Here, we are only concerned with if various pairs of straws are connected by a path of
touching straws. You will be given a list of the endpoints for some straws (as if they were dumped on a large piece of graph paper) and then will be asked if various pairs of straws are connected. Note that touching is connecting, but also two straws can be
connected indirectly via other connected straws.
Input

Input consist multiple case,each case consists of multiple lines. The first line will be an integer n (1 < n < 13) giving the number of straws on the table. Each of the next n lines contain 4 positive integers,x1,y1,x2 and y2, giving the coordinates, (x1,y1),(x2,y2)
of the endpoints of a single straw. All coordinates will be less than 100. (Note that the straws will be of varying lengths.) The first straw entered will be known as straw #1, the second as straw #2, and so on. The remaining lines of the current case(except
for the final line) will each contain two positive integers, a and b, both between 1 and n, inclusive. You are to determine if straw a can be connected to straw b. When a = 0 = b, the current case is terminated. 

When n=0,the input is terminated. 

There will be no illegal input and there are no zero-length straws. 

Output

You should generate a line of output for each line containing a pair a and b, except the final line where a = 0 = b. The line should say simply "CONNECTED", if straw a is connected to straw b, or "NOT CONNECTED", if straw a is not connected to straw b. For
our purposes, a straw is considered connected to itself.
Sample Input

7
1 6 3 3
4 6 4 9
4 5 6 7
1 4 3 5
3 5 5 5
5 2 6 3
5 4 7 2
1 4
1 6
3 3
6 7
2 3
1 3
0 0

2
0 2 0 0
0 0 0 1
1 1
2 2
1 2
0 0

0

Sample Output

CONNECTED
NOT CONNECTED
CONNECTED
CONNECTED
NOT CONNECTED
CONNECTED
CONNECTED
CONNECTED
CONNECTED

Source

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
const int N = 1e4+10;
struct node
{
double x1, y1, x2, y2;
} p
;
const double eps=1e-10;
double det(int i,double x,double y)//外积
{
double x1=p[i].x1-x, y1=p[i].y1-y;
double x2=p[i].x2-x, y2=p[i].y2-y;
return add(x1*y2,-x2*y1);
}
int judge(int i,int j)
{

int l1=min(p[i].x1,p[i].x2), l2=max(p[i].x1,p[i].x2);
int l3=min(p[i].y1,p[i].y2), l4=max(p[i].y1,p[i].y2);
int l5=min(p[j].x1,p[j].x2), l6=max(p[j].x1,p[j].x2);
int l7=min(p[j].y1,p[j].y2), l8=max(p[j].y1,p[j].y2);
if(l2<l5||l6<l1||l4<l7||l8<l3) return 0;
return (det(i,p[j].x1,p[j].y1)*det(i,p[j].x2,p[j].y2))<=0&&(det(j,p[i].x1,p[i].y1)*det(j,p[i].x2,p[i].y2)<=0);
}

int w[200][200];

int main()
{
int n;
while(scanf("%d", &n),n!=0)
{
for(int i=1; i<=n; i++)
{
scanf("%lf %lf %lf %lf", &p[i].x1, &p[i].y1, &p[i].x2, &p[i].y2);
}
memset(w,0,sizeof(w));
for(int i=1; i<=n; i++)
{
for(int j=i; j<=n; j++)
if(judge(i,j)) w[i][j]=w[j][i]=1;
}
for(int k=1; k<=n; k++)
{
for(int i=1; i<=n; i++)
{
for(int j=1; j<=n; j++)
{
w[i][j]|=(w[i][k]&&w[k][j]);
w[j][i]=w[i][j];
}
}
}
int x, y;
while(scanf("%d %d", &x, &y),x!=0||y!=0)
{
if(w[x][y]) printf("CONNECTED\n");
else printf("NOT CONNECTED\n");
}
}
return 0;
}