1 /*cug_1078判断线段是否有交点并求交点*/
2 #include <stdio.h>
3 #include <stdlib.h>
4 #include <math.h>
5
6 const double eps = 1e-6;
7
8 typedef struct TPodouble
9 {
10 double x;
11 double y;
12 }TPodouble;
13
14 typedef struct TLine
15 {
16 double a, b, c;
17 }TLine;
18
19 double max(double x, double y)
20 {
21 if(x > y) return x;
22 else return y;
23 }
24
25 double min(double x, double y)
26 {
27 if(x < y) return x;
28 else return y;
29 }
30 double multi(TPodouble p1, TPodouble p2, TPodouble p0)
31 {
32 return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
33 }
34
35 TLine lineFromSegment(TPodouble p1, TPodouble p2)
36 {
37 TLine tmp;
38 tmp.a = p2.y - p1.y;
39 tmp.b = p1.x - p2.x;
40 tmp.c = p2.x * p1.y - p1.x * p2.y;
41 return tmp;
42 }
43
44 void Linedoubleer(TLine l1, TLine l2)
45 {
46 double x, y;
47 double a1 = l1.a;
48 double b1 = l1.b;
49 double c1 = l1.c;
50 double a2 = l2.a;
51 double b2 = l2.b;
52 double c2 = l2.c;
53 if(b1 == 0){
54 x = -c1 / (double)a1;
55 y = (-c2 - a2 * x) / (double)b2;
56 }
57 else{
58 x = (double)(c1 * b2 - b1 * c2) / (double)(b1 * a2 - b2 * a1);
59 y = (double)(-c1 - a1 * x) /(double)b1;
60 }
61 printf("%.3lf %.3lf\n", x, y);
62 }
63
64 bool isIntersected(TPodouble s1, TPodouble e1, TPodouble s2, TPodouble e2){
65
66 if(
67 (max(s1.x, e1.x) >= min(s2.x, e2.x)) &&
68 (max(s2.x, e2.x) >= min(s1.x, e1.x)) &&
69 (max(s1.y, e1.y) >= min(s2.y, e2.y)) &&
70 (max(s2.y, e2.y) >= min(s1.y, e1.y)) &&
71 (multi(s2, e1, s1) * multi(e1, e2, s1) >= 0) &&
72 (multi(s1, e2, s2) * multi(e2, e1, s2) >= 0)
73 ) return true;
74
75 return false;
76 }
77
78 double dis(TPodouble a, TPodouble b)
79 {
80 return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
81 }
82
83 int ISSAME(TPodouble a, TPodouble b)
84 {
85 if(fabs(a.x - b.x) > eps) return 0;
86 if(fabs(a.y - b.y) > eps) return 0;
87 return 1;
88 }
89
90 void between(TPodouble s1, TPodouble e1, TPodouble s2, TPodouble e2)
91 {
92 double d1 = dis(s1, s2);
93 double d2 = dis(s1, e2);
94 double d3 = dis(e1, s2);
95 double d4 = dis(e1, e2);
96 double d5 = dis(s1, e1);
97 double d6 = dis(s2, e2);
98 if(ISSAME(s1, s2) && fabs(d5 + d6 - d4) < eps) printf("%.3lf %.3lf\n", s1.x, s1.y);
99 else if(ISSAME(s1, e2) && fabs(d3 - d5 - d6) < eps) printf("%.3lf %.3lf\n", s1.x, s1.y);
100 else if(ISSAME(e1, s2) && fabs(d2 - d5 - d6) < eps) printf("%.3lf %.3lf\n", s2.x, s2.y);
101 else if(ISSAME(e1, e2) && fabs(d1 - d5 - d6) < eps) printf("%.3lf %.3lf\n", e2.x, e2.y);
102 else printf("Too much points in common\n");
103 }
104
105 int main()
106 {
107 TPodouble s1, e1, s2, e2;
108 TLine l1, l2;
109 while(scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &s1.x, &s1.y, &e1.x, &e1.y, &s2.x, &s2.y, &e2.x, &e2.y) != EOF){
110 if(fabs((s1.y - e1.y) * (s2.x - e2.x) - (s1.x - e1.x) * (s2.y - e2.y)) < eps){
111 l1 = lineFromSegment(s1, e1);
112 l2.c = -(l1.a * s2.x + l1.b * s2.y);
113 if(fabs((l1.c - l2.c) / sqrt((double)l1.a * l1.a + l1.b * l1.b)) > 0){
114 printf("No point in common\n");
115 }
116 else {
117 if(!isIntersected(s1, e1, s2, e2)) printf("No point in common\n");
118 else between(s1, e1, s2, e2);
119 }
120 }
121 else {
122 if(isIntersected(s1, e1, s2, e2)){
123 l1 = lineFromSegment(s1, e1);
124 l2 = lineFromSegment(s2, e2);
125 Linedoubleer(l1, l2);
126 }
127 else printf("No point in common\n");
128 }
129 }
130 return 0;
131 }
