POJ - 2653 - Pick-up sticks 线段与线段相交

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <vector>
 4 #include <cmath>
 5 #include <cstring>
 6 using namespace std;
 7 const double eps = 1e-8;
 8 int dcmp(double x)
 9 {
10     return fabs(x) < eps ? 0 : (x < 0 ? -1 : 1);
11 }
12 struct Point 
13 {
14     double x,y;
15     Point(double a = 0, double b = 0) : x(a), y(b) {}
16 };
17 Point operator - (Point a, Point b)
18 {
19     return Point(a.x-b.x, a.y-b.y);
20 }
21 double Det(Point a, Point b)
22 {
23     return a.x * b.y - a.y * b.x;
24 }
25 double Dot(Point a, Point b)
26 {
27     return a.x*b.x + a.y*b.y;
28 }
29 bool OnSegment(Point p, Point a1, Point a2)
30 {
31     return dcmp(Det(a1 - p, a2 - p)) == 0 && dcmp(Dot(a1 - p, a2 - p)) <= 0;
32 }
33 bool SegCross(Point a1, Point a2, Point b1, Point b2)
34 {
35     double c1 = Det(a2 - a1, b1 - a1);
36     double c2 = Det(a2 - a1, b2 - a1);
37     double c3 = Det(b2 - b1, a1 - b1);
38     double c4 = Det(b2 - b1, a2 - b1);
39     if (dcmp(c1) * dcmp(c2) < 0 && dcmp(c3) * dcmp(c4) < 0) return 1;
40     else if (OnSegment(b1, a1, a2) ) return 1;
41     else if (OnSegment(b2, a1, a2) ) return 1;
42     else if (OnSegment(a1, b1, b2) ) return 1;
43     else if (OnSegment(a2, b1, b2) ) return 1;
44     else return 0;
45 }
46 
47 struct Line
48 {
49     Point s,e;
50     Line() {}
51     Line(Point a,Point b) : s(a), e(b) {}
52 }l[100005];
53 int res[1005];
54 int main()
55 {
56     int n;
57     while (~scanf("%d", &n) && n)
58     {
59         for (int i = 1; i <= n; i++){
60             scanf("%lf%lf%lf%lf", &l[i].e.x, &l[i].e.y, &l[i].s.x, &l[i].s.y);
61         }
62         int cnt = 0;
63         for(int i = 1; i <= n; i++)
64         {
65             bool flag = 1;
66             for (int j = i+1; j <= n; j++)
67             {
68                 if(SegCross(l[i].e, l[i].s, l[j].e, l[j].s)){
69                     flag = 0; break;
70                 }
71             }
72             if(flag) res[cnt++] = i;
73         }
74                     
75         printf("Top sticks: ");
76         for (int i = 0; i < cnt-1; i++)
77             printf("%d, ", res[i]);
78         printf("%d.\n", res[cnt-1]);
79     }
80 }