算法模板——Dinic网络最大流 2

 1 type
 2     point=^node;
 3     node=record
 4                g,w:longint;
 5                next,anti:point;
 6     end;
 7 var
 8    i,j,k,l,m,n,s,t,flow:longint;
 9    a,e:array[0..10000] of point;
10    c,d:array[0..10000] of longint;
11 function min(x,y:longint):longint;
12          begin
13               if x<y then min:=x else min:=y;
14          end;
15 procedure add(x,y,z:longint);
16           var p:point;
17           begin
18                new(p);p^.g:=y;p^.w:=z;p^.next:=a[x];a[x]:=p;
19                new(p);p^.g:=x;p^.w:=0;p^.next:=a[y];a[y]:=p;
20                a[x]^.anti:=a[y];a[y]^.anti:=a[x];
21           end;
22 function spfa:boolean;
23          var p:point;f,r:longint;
24          begin
25               fillchar(c,sizeof(c),255);
26               d[1]:=s;f:=1;r:=2;c[s]:=0;
27               while f<r do
28                     begin
29                          p:=a[d[f]];
30                          while p<>nil do
31                                begin
32                                     if (p^.w<>0) and (c[p^.g]=-1) then
33                                        begin
34                                             c[p^.g]:=c[d[f]]+1;
35                                             e[p^.g]:=p;
36                                             d[r]:=p^.g;inc(r);
37                                        end;
38                                     p:=p^.next;
39                                end;
40                          inc(f);
41                     end;
42               exit(c[t]<>-1);
43          end;
44 procedure calc;   //“顺藤摸瓜”模式有效避免了递归带来的爆栈隐患
45           begin
46                i:=t;l:=maxlongint;
47                while i<>s do
48                      begin
49                           l:=min(l,e[i]^.w);
50                           i:=e[i]^.anti^.g;
51                      end;
52                i:=t;inc(flow,l);
53                while i<>s do
54                      begin
55                           if e[i]^.w<>maxlongint then dec(e[i]^.w,l);
56                           if e[i]^.anti^.w<>maxlongint then inc(e[i]^.anti^.w,l);
57                           i:=e[i]^.anti^.g;
58                      end;
59           end;
60 begin
61      readln(m,n,s,t);
62      for i:=1 to n do a[i]:=nil;
63      for i:=1 to m do
64          begin
65               readln(j,k,l);
66               add(j,k,l);
67          end;
68      flow:=0;while spfa do calc;
69      writeln(flow);
70      readln;
71 end.