算法模板——sap网络最大流 2

实现功能：同最大流 1

这里面主要是把前面的邻接矩阵改成了邻接表，相比之下速度大大提高——本人实测，当M=1000000 N=10000 时，暂且不考虑邻接矩阵会不会MLE，新的程序速度快了很多倍（我们家这个很弱的电脑上耗时0.3s）；而当M=300000 N=10000时，优势更加明显（几乎是秒出），别的没了，尤其当遇到稀疏图的时候这样子是大大划算的！！！

  1 type
  2     point=^node;
  3     node=record
  4                g,w:longint;
  5                next:point;
  6     end;
  7
  8 var
  9    i,j,k,l,m,n,tmp,ans,aug,mi,s,t:longint;
 10    di,a:array[0..10005] of point;
 11    pre,his,dis,vh:array[0..10005] of longint;
 12    flag:boolean;p,jl:point;
 13 function min(x,y:longint):longint;inline;
 14          begin
 15               if x<y then  min:=x else min:=y;
 16          end;
 17 function add(x,y,z:longint):longint;inline;
 18           var p:point;
 19           begin
 20                new(p);p^.w:=z;p^.g:=y;
 21                p^.next:=a[x];a[x]:=p;
 22           end;
 23 procedure op(x,y,z:longint);inline;
 24           var p:point;
 25           begin
 26                p:=a[x];
 27                while p<>nil do
 28                      begin
 29                           if (p^.g=y) and ((p^.w+z)>=0) then
 30                              begin
 31                                   p^.w:=p^.w+z;
 32                                   break;
 33                              end;
 34                           p:=p^.next;
 35                      end;
 36           end;
 37 begin
 38      readln(n,m,s,t);
 39      for i:=1 to n do a[i]:=nil;
 40      for i:=1 to m do
 41          begin
 42               readln(j,k,l);
 43               add(j,k,l);add(k,j,0);
 44          end;
 45      for i:=1 to n do di[i]:=a[i];
 46      fillchar(dis,sizeof(dis),0);
 47      fillchar(pre,sizeof(pre),0);
 48      fillchar(his,sizeof(his),0);
 49      fillchar(vh,sizeof(vh),0);
 50      i:=s;vh[0]:=n;ans:=0;aug:=maxlongint;
 51      while dis[s]<n do
 52            begin
 53                 flag:=false;his[i]:=aug;
 54                 p:=a[i];
 55                 while p<>nil do
 56                       begin
 57                            if (p^.w>0) and (dis[i]=(dis[p^.g]+1)) then
 58                               begin
 59                                    aug:=min(aug,p^.w);
 60                                    pre[p^.g]:=i;di[i]:=p;
 61                                    flag:=true;i:=p^.g;
 62                                    if i=t then
 63                                       begin
 64                                            ans:=ans+aug;
 65                                            while i<>s do
 66                                                  begin
 67                                                       tmp:=i;
 68                                                       i:=pre[i];
 69                                                       op(i,tmp,-aug);
 70                                                       op(tmp,i,aug);
 71                                                  end;
 72                                            aug:=maxlongint;
 73                                       end;
 74                                    break;
 75                               end;
 76                            p:=p^.next;
 77                       end;
 78                 if flag then continue;
 79                 jl:=nil;mi:=n-1;
 80                 p:=a[i];
 81                 while p<>nil do
 82                       begin
 83                            if (p^.w>0) and (dis[p^.g]<mi) then
 84                               begin
 85                                    jl:=p;mi:=dis[p^.g];
 86                               end;
 87                            p:=p^.next;
 88                       end;
 89                 di[i]:=jl;
 90                 dec(vh[dis[i]]);
 91                 if vh[dis[i]]=0 then break;
 92                 dis[i]:=mi+1;
 93                 inc(vh[dis[i]]);
 94                 if i<>s then
 95                    begin
 96                         i:=pre[i];
 97                         aug:=his[i];
 98                    end;
 99            end;
100      writeln(ans);
101 end.
102