[POJ2135]最小费用最大流

program poj2135;
const maxn=1010;maxm=50010;
var n,m,i,j,x,y,z:longint;
      link,opt,dis,pre:array[-1..maxn]of longint;
      vis:array[-1..maxn]of boolean;
      fa,from,next,w,c,rev:array[-1..maxm]of longint;

function min(a,b:longint):longint;
begin
    if a<b then exit(a) else exit(b);
end;

procedure add(x,y,z,cc:longint);
begin
    inc(j);fa[j]:=y;from[j]:=x;next[j]:=link[x];link[x]:=j;w[j]:=z;c[j]:=cc;rev[j]:=j+1;
    inc(j);fa[j]:=x;from[j]:=y;next[j]:=link[y];link[y]:=j;w[j]:=-z;c[j]:=0;rev[j]:=j-1;
end;
    
function spfa:boolean;
var head,tail,x,j:longint;
begin
    fillchar(dis,sizeof(dis),63);
    fillchar(vis,sizeof(vis),true);
    head:=0;tail:=1;
    opt[1]:=0;vis[0]:=false;dis[0]:=0;
    while head<>tail do 
    begin
        head:=(head+1) mod maxn;
        x:=opt[head];j:=link[x];
        while j<>0 do 
        begin
            if (c[j]>0)and(dis[x]+w[j]<dis[fa[j]]) then
            begin
                dis[fa[j]]:=dis[x]+w[j];
                pre[fa[j]]:=j;
                if vis[fa[j]] then
                begin
                    tail:=(tail+1) mod maxn;
                    opt[tail]:=fa[j];
                end;
            end;
            j:=next[j];
        end;
        vis[x]:=true;
    end;
    if dis[n+1]<>dis[-1] then exit(true) else exit(false);
end;

function MCMF:longint;
var ans,x,sum:longint;
begin
    ans:=0;
    while spfa do
    begin
        sum:=maxlongint;
        x:=n+1;
        while x<>0 do 
        begin
            sum:=min(sum,c[pre[x]]);
            x:=from[pre[x]];
        end;
        x:=n+1;
        while x<>0 do 
        begin
            inc(ans,sum*w[pre[x]]);
            dec(c[pre[x]],sum);
            inc(c[rev[pre[x]]],sum);
            x:=from[pre[x]];
        end;
    end;
    exit(ans);
end;

begin
    assign(input,‘poj2135.in‘);reset(input);
    readln(n,m);j:=0;
    for i:=1 to m do 
    begin
        readln(x,y,z);
        add(x,y,z,1);add(y,x,z,1);
    end;
    add(0,1,0,2);add(n,n+1,0,2);
    writeln(MCMF);
end.