POJ 2588(解析几何+并查集）

题目就是早从左到右的路

注意输入的实数

这题图画好就行，别像我一开始把图弄反就成

从上开始找，若找到一个与下边界相邻的就无解，找到与左边相邻的记圆与左边界相交的下边的点（相当于左上角挖去一块），右边同理。

Program snake;const   maxn=1000;var   n,i,j:longint;   x,y,r,lc,rc:array[1..maxn] of double;   maxl,maxr:double;   father:array[1..maxn] of longint;   b,up,down,left,right:array[1..maxn] of boolean;function getfather(x:longint):longint;begin   if father[x]=x then exit(x);   father[x]:=getfather(father[x]);   exit(father[x]);end;Procedure union(x,y:longint);begin   father[father[x]]:=father[father[y]];end;function distance(i,j:longint):double;begin   exit(sqrt(sqr(x[i]-x[j])+sqr(y[i]-y[j])));end;function dis(x1,y1,x2,y2:double):double;begin   exit(sqrt(sqr(x1-x2)+sqr(y1-y2)));end;begin   fillchar(b,sizeof(b),false);   fillchar(up,sizeof(up),false);   fillchar(down,sizeof(down),false);   fillchar(left,sizeof(left),false);   fillchar(right,sizeof(right),false);   fillchar(lc,sizeof(lc),0);   fillchar(rc,sizeof(rc),0);   maxl:=1000;maxr:=1000;   read(n);   for i:=1 to n do   begin      read(x[i],y[i],r[i]);      father[i]:=i;      for j:=1 to i-1 do         if distance(i,j)<r[i]+r[j] then            if getfather(i)<>getfather(j) then               union(i,j);      if (y[i]<r[i]) then down[i]:=true;      if (y[i]+r[i]>1000) then up[i]:=true;      if (x[i]<r[i]) then      begin         left[i]:=true;         lc[i]:=y[i]-sqrt(sqr(r[i])-sqr(x[i]));      end;      if (x[i]+r[i]>1000) then      begin         right[i]:=true;         rc[i]:=y[i]-sqrt(sqr(r[i])-sqr(1000-x[i]));      end;   end;   for i:=1 to n do      if (up[i]) and not(b[i]) then      begin         for j:=1 to n do            if father[i]=father[j] then            begin               b[j]:=true;               if (down[j]) then               begin                  writeln('Bill will be bitten.');                  halt;               end;               if left[j] then               begin                  if lc[j]<maxl then maxl:=lc[j];               end;               if right[j] then               begin                  if rc[j]<maxr then maxr:=rc[j];               end;            end;      end;   writeln('Bill enters at (0.00, ',maxl:2:2,') and leaves at (1000.00, ',maxr:2:2,').');end.