POJ 2653--Pick-up sticks(判断线段相交)

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<cstdio>
 4 #include<cstdlib>
 5 using namespace std;
 6 const int MAX = 100000;
 7 typedef struct point {
 8     double x;
 9     double y;
10     point() {
11 
12     }
13     point(double a, double b) {
14         x = a;
15         y = b;
16     }
17 }point;
18 typedef struct edge {
19     point start;
20     point end;
21     edge() {
22 
23     }
24     edge(point a, point b) {
25         start = a;
26         end = b;
27     }
28 }edge;
29 edge line[MAX], tmp;
30 point p;
31 int n;
32 double x, y, x2, y2;
33 inline double max(double a, double b) { return a > b ? a : b; }
34 inline double min(double a, double b) { return a < b ? a : b; }
35 double multi(point p1, point p2, point p0) {
36     return (p2.y - p0.y)*(p1.x - p0.x) - (p2.x - p0.x)*(p1.y - p0.y);
37 }
38 bool Across(edge v1, edge v2) {
39     if (max(v1.start.x, v1.end.x) >= min(v2.start.x, v2.end.x) &&
40         max(v2.start.x, v2.end.x) >= min(v1.start.x, v1.end.x) &&
41         max(v1.start.y, v1.end.y) >= min(v2.start.y, v2.end.y) &&
42         max(v2.start.y, v2.end.y) >= min(v1.start.y, v1.end.y) &&
43         multi(v1.start, v2.end, v2.start)*multi(v2.end, v1.end, v2.start) > 0 &&
44         multi(v2.start, v1.end, v1.start)*multi(v1.end, v2.end, v1.start) > 0
45         )
46         return true;
47     return false;
48 }
49 int main(void) {
50     while (~scanf("%d", &n) && n) {
51         for (int i = 0; i < n; i++) {
52             scanf("%lf%lf%lf%lf", &x, &y, &x2, &y2);
53             line[i] = edge(point(x, y), point(x2, y2));
54         }
55         printf("Top sticks:");
56         for (int i = 0; i < n-1; i++) {        //最后一根木棒必定在上面
57             tmp = line[i];
58             int flag = 0;
59             for (int j = i + 1; j < n; j++) {
60                 if (Across(tmp, line[j]))    //和之后的木块相交，一定在下面
61                 {
62                     flag = 1;
63                     break;
64                 }
65             }
66             if (flag != 1) {
67                 printf(" %d,", i + 1);
68             }
69         }
70         printf(" %d.\n", n);
71     }
72     return 0;
73 }