算法模板——sap网络最大流 1（非递归+邻接矩阵）

实现功能：首行输入N，M，S，T，代表这张图N个点，M条边，源点为S，汇点为T；接下来T行输入个边的出发点、终点和权值；输出最大流

原理：sap网络流算法（详见百度百科，个人觉得这个模板已经不错了，虽然本人暂时还未考虑引入邻接表进行优化）（推荐模板题：Codevs1993）

 1 var
 2    i,j,k,l,m,n,ans,aug,s,t,tmp,jl,mi:longint;
 3    flag:boolean;
 4    vh,dis,di,his,pre:array[0..10000] of longint;
 5    map:array[0..2050,0..2050] of longint;
 6 function min(x,y:longint):longint;inline;
 7          begin
 8               if x<y then min:=x else min:=y;
 9          end;
10 begin
11      readln(n,m,s,t);
12      fillchar(map,sizeof(map),0);
13      for i:=1 to m do
14          begin
15               readln(j,k,l);
16               map[j,k]:=map[j,k]+l;
17          end;
18      i:=s;ans:=0;aug:=maxlongint;
19      fillchar(dis,sizeof(dis),0);
20      for i:=1 to n do di[i]:=1;
21      i:=s;
22      while dis[s]<n do
23            begin
24                 flag:=false;
25                 his[i]:=aug;
26                 for j:=di[i] to n do
27                     begin
28                          if (map[i,j]>0) and (dis[i]=(dis[j]+1)) then
29                             begin
30                                  aug:=min(aug,map[i,j]);
31                                  pre[j]:=i;di[i]:=j;
32                                  i:=j;flag:=true;
33                                  if i=t then
34                                     begin
35                                          ans:=ans+aug;
36                                          while i<>s do
37                                                begin
38                                                     tmp:=i;
39                                                     i:=pre[i];
40                                                     map[i,tmp]:=map[i,tmp]-aug;
41                                                     map[tmp,i]:=map[tmp,i]+aug;
42                                                end;
43                                          aug:=maxlongint;
44                                     end;
45                                  break;
46                             end;
47                     end;
48                 if flag then continue;
49                 jl:=-1;mi:=n-1;
50                 for j:=1 to n do
51                     begin
52                          if (map[i,j]>0) and (dis[j]<mi) then
53                             begin
54                                  mi:=dis[j];
55                                  jl:=j;
56                             end;
57                     end;
58                 di[i]:=jl;
59                 dec(vh[dis[i]]);
60                 if vh[dis[i]]=0 then break;
61                 dis[i]:=mi+1;
62                 inc(vh[dis[i]]);
63                 if i<>s then
64                    begin
65                         i:=pre[i];
66                         aug:=his[i];
67                    end;
68            end;
69      writeln(ans);
70 end.
71