P1631: [Usaco2007 Feb]Cow Party
还是水题，接近于裸的spfa（个人比较喜欢用spfa，dijkstra不太喜欢用），代码附上
1 const maxn=6200001;
2 type
3 link=^node;
4 node=record
5 t,d:longint;
6 f:link;
7 end;
8 var n,m,s,i,j,u,v,w,max:longint;
9 adj:array[0..3000] of link;
10 f:array[0..1000000] of longint;
11 d,val:array[0..3000] of longint;
12 went:array[0..3000] of boolean;
13 procedure insert(f,t,d:longint);
14 var p:link;
15 begin
16 new(p);
17 p^.f:=adj[f];
18 p^.t:=t;
19 p^.d:=d;
20 adj[f]:=p;
21 end;
22 procedure spfa(s:longint);
23 var l,r,now,i:longint;
24 p:link;
25 begin
26 for i:=1 to n do
27 d[i]:=maxn;
28 fillchar(went,sizeof(went),true);
29 l:=1; r:=1; f[1]:=s; d[s]:=0; went[s]:=false;
30 while l<=r do
31 begin
32 now:=f[l];
33 p:=adj[now];
34 while p<>nil do
35 begin
36 if d[p^.t]>d[now]+p^.d then
37 begin
38 d[p^.t]:=d[now]+p^.d;
39 if went[p^.t] then
40 begin
41 went[p^.t]:=false;
42 inc(r);
43 f[r]:=p^.t;
44 end;
45 end;
46 p:=p^.f;
47 end;
48 went[now]:=true;
49 inc(l);
50 end;
51 end;
52 begin
53 readln(n,m,s);
54 for i:=1 to m do
55 begin
56 readln(u,v,w);
57 insert(u,v,w);
58 //insert(v,u,w);
59 end;
60 for i:=1 to n do
61 begin
62 spfa(i);
63 val[i]:=d[s];
64 //writeln(sb);
65 //writeln(d[s]);
66 end;
67 spfa(s);
68 for i:=1 to n do
69 //if i<>s then
70 begin
71 inc(val[i],d[i]);
72 if val[i]>max then max:=val[i];
73 end;
74 writeln(max);
75 end.
(转载请注明出处：http://www.cnblogs.com/Kalenda/)
