poj2074Line of Sight(直线相交）

  1 #include <iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<algorithm>
  5 #include<stdlib.h>
  6 #include<vector>
  7 #include<cmath>
  8 #include<queue>
  9 #include<set>
 10 using namespace std;
 11 #define N 10100
 12 #define LL long long
 13 #define INF 0xfffffff
 14 #define zero(x) (((x)>0?(x):-(x))<eps)
 15 const double eps = 1e-8;
 16 const double pi = acos(-1.0);
 17 const double inf = ~0u>>2;
 18 struct point
 19 {
 20     double x,y;
 21     point(double x=0,double y=0):x(x),y(y) {}
 22 } p[N];
 23 struct line
 24 {
 25     point u,v;
 26 } li[N];
 27 typedef point pointt;
 28 pointt operator -(point a,point b)
 29 {
 30     return point(a.x-b.x,a.y-b.y);
 31 }
 32 int dcmp(double x)
 33 {
 34     if(fabs(x)<eps) return 0;
 35     return x<0?-1:1;
 36 }
 37 bool cmp(point a,point b)
 38 {
 39     if(dcmp(a.x-b.x)==0)
 40         return a.y<b.y;
 41     return a.x<b.x;
 42 }
 43 
 44 bool intersection1(point p1, point p2, point p3, point p4, point& p)      // 直线相交
 45 {
 46     double a1, b1, c1, a2, b2, c2, d;
 47     a1 = p1.y - p2.y;
 48     b1 = p2.x - p1.x;
 49     c1 = p1.x*p2.y - p2.x*p1.y;
 50     a2 = p3.y - p4.y;
 51     b2 = p4.x - p3.x;
 52     c2 = p3.x*p4.y - p4.x*p3.y;
 53     d = a1*b2 - a2*b1;
 54     if (!dcmp(d))    return false;
 55     p.x = (-c1*b2 + c2*b1) / d;
 56     p.y = (-a1*c2 + a2*c1) / d;
 57     return true;
 58 }
 59 int main()
 60 {
 61     int i,n;
 62     int x1,x2,y;
 63     while(scanf("%d%d%d",&x1,&x2,&y)&&x1&&x2&&y)
 64     {
 65         li[1].u = point(x1,y);
 66         li[1].v = point(x2,y);
 67         li[1].v.y = li[1].u.y;
 68         scanf("%lf%lf%lf",&li[2].u.x,&li[2].v.x,&li[2].u.y);
 69         li[2].v.y = li[2].u.y;
 70         scanf("%d",&n);
 71         for(i = 3; i <= n+2; i++)
 72         {
 73             scanf("%lf%lf%lf",&li[i].u.x,&li[i].v.x,&li[i].u.y);
 74             li[i].v.y = li[i].u.y;
 75         }
 76         n+=2;
 77         int g = 0;
 78         for(i = 3 ; i <= n; i++)
 79         {
 80             if(dcmp(li[i].u.y-li[1].u.y)>=0||dcmp(li[i].u.y-li[2].u.y)<=0) continue;
 81             point pp;
 82             intersection1(li[1].u,li[i].v,li[2].u,li[2].v,pp);
 83             p[++g].y = min(li[2].v.x,max(pp.x,li[2].u.x));
 84             intersection1(li[1].v,li[i].u,li[2].u,li[2].v,pp);
 85             p[g].x = max(li[2].u.x,min(li[2].v.x,pp.x));
 86         }
 87         sort(p+1,p+g+1,cmp);
 88         double maxz,ty ;
 89        // cout<<p[1].x<<" "<<p[1].y<<endl;
 90         if(g==0)
 91         maxz = li[2].v.x-li[2].u.x;
 92         else
 93         {
 94             maxz = max(p[1].x-li[2].u.x,li[2].v.x-p[g].y);
 95             ty = p[1].y;
 96         }
 97 
 98         for(i = 1; i < g; i++)
 99         {
100            // printf("%.3f %.3f\n",p[i].x,p[i].y);
101             ty = max(ty,p[i].y);
102             if(p[i+1].x>ty)
103             {
104                 maxz = max(p[i+1].x-ty,maxz);//printf("%.3f %.3f\n",ty,maxz);
105                 ty = p[i+1].y;
106             }
107 
108         }
109         if(dcmp(maxz)<=0)
110             puts("No View");
111         else
112             printf("%.2f\n",maxz);
113     }
114     return 0;
115 }
116 /*
117 2 6 6
118 0 15 0
119 3
120 1 2 1
121 3 4 1
122 12 13 1
123 1 5 5
124 0 10 0
125 1
126 0 15 1
127 2 6 6
128 0 15 0
129 3
130 1 2 1
131 3 4 1
132 12 13 1
133 2 6 6
134 0 15 0
135 4
136 1 2 1
137 3 4 1
138 12 13 1
139 1 5 2
140 2 6 6
141 0 15 0
142 2
143 0 5 3
144 6 15 3
145 2 6 6
146 0 15 0
147 2
148 6 10 1
149 0 2 1
150 2 6 6
151 0 15 0
152 1
153 2 6 7
154 2 6 6
155 0 15 0
156 1
157 2 6 7
158 2 6 6
159 0 15 0
160 1
161 4 4.5 5.5
162 2 6 6
163 0 15 0
164 16
165 0 1 3
166 1.5 2 3
167 2.5 3 3
168 3.5 4 3
169 4.5 5 3
170 5.5 6 3
171 6.5 7 3
172 7.5 8 3
173 8.5 9 3
174 9.5 10 3
175 10.5 11 3
176 11.5 12 3
177 12.5 13 3
178 13.5 14 3
179 14.5 15 3
180 15.5 16 3
181 2 6 6
182 0 15 0
183 16
184 0 1 .1
185 1.5 2 .1
186 2.5 3 .1
187 3.5 4 .1
188 4.5 5 .1
189 5.5 6 .1
190 6.5 7 .1
191 7.5 8 .1
192 8.5 9 .1
193 9.5 10 .1
194 10.5 11 .1
195 11.5 12 .1
196 12.5 13 .1
197 13.5 14 .1
198 14.5 15 .1
199 15.5 16 .1
200 2 6 6
201 0 15 0
202 14
203 0 1 3
204 1.5 2 3
205 2.5 3 3
206 3.5 4 3
207 4.5 5 3
208 5.5 6 3
209 8.5 9 3
210 9.5 10 3
211 10.5 11 3
212 11.5 12 3
213 12.5 13 3
214 13.5 14 3
215 14.5 15 3
216 15.5 16 3
217 2 6 6
218 0 4000000000 0
219 2
220 1 2 1 
221 15 16 3
222 2 6 6
223 0 15 1
224 5
225 1 1.5 6
226 17 18 1 
227 3 5 3
228 0 20 10
229 0 20 0.5
230 
231 答案：
232 8.80
233 No View
234 8.80
235 6.70
236 No View
237 4.00
238 15.00
239 15.00
240 No View
241 No View
242 0.44
243 1.00
244 3999999970.00
245 8.00
246 */