P3390: [Usaco2004 Dec]Bad Cowtractors牛的报复

 1 type
 2   node=record
 3     f,t,l:longint;
 4   end;
 5 var n,m,i,j,fx,fy,num,ans:longint;
 6 b:array[0..20001] of node;
 7 father:array[0..1001] of longint;
 8 procedure qs(t,w:longint);
 9 var mid,l,r:longint;
10 tem:node;
11 begin
12   l:=t; r:=w; mid:=b[(l+r) shr 1].l;
13   repeat
14     begin
15       while b[l].l>mid do inc(l);
16       while b[r].l<mid do dec(r);
17       if l<=r then
18         begin
19           tem:=b[l];
20           b[l]:=b[r];
21           b[r]:=tem;
22           inc(l);
23           dec(r);
24         end;
25     end;
26   until l>r;
27   if t<r then qs(t,r);
28   if l<w then qs(l,w);
29 end;
30 function findfather(x:longint):longint;
31 begin
32   if x=father[x] then exit(x)
33     else father[x]:=findfather(father[x]);
34   exit(father[x]);
35 end;
36 begin
37   readln(n,m);
38   for i:=1 to m do
39     with b[i] do
40       readln(f,t,l);
41   qs(1,m); num:=0;
42   for i:=1 to n do
43     father[i]:=i;
44   for i:=1 to m do
45     begin
46       fx:=findfather(b[i].f);
47       fy:=findfather(b[i].t);
48       if fx<>fy then
49         begin
50           father[fx]:=fy;
51           inc(ans,b[i].l);
52           inc(num);
53         end;
54       if num=n-1 then
55         begin
56           writeln(ans);
57           halt;
58         end;
59     end;
60   writeln(-1);
61 end.