SPFA算法模板

const maxp=10000; {最大结点数}
var p,c,s,t:longint; {p,结点数;c,边数;s:起点;t:终点}
　   a,b:array[1..maxp,0..maxp] of longint; {a[x,y]存x,y之间边的权;b[x,c]存与x相连的第c个边的另一个结点y}
　   d:array[1..maxp] of integer; {队列}
　   v:array[1..maxp] of boolean; {是否入队的标记}
　   dist:array[1..maxp] of longint; {到起点的最短路}
　   head,tail:longint; {队首/队尾指针}
procedure init;
var i,x,y,z:longint;
begin
  read(p,c); 
  for i := 1 to c do
   begin
     readln(x,y,z); {x,y:一条边的两个结点;z:这条边的权值}
     inc(b[x,0]); b[x,b[x,0]] := y; a[x,y] := z; {b[x,0]：以x为一个结点的边的条数}
     inc(b[y,0]); b[y,b[y,0]] := x; a[y,x] := z;
   end;
  readln(s,t); {读入起点与终点}
end;
procedure spfa(s:longint); {SPFA}
var i,j,now,sum:longint;
begin
  fillchar(d,sizeof(d),0);
  fillchar(v,sizeof(v),false);
  for j := 1 to p do dist[ j ]:=maxlongint;
  dist[s] := 0; v[s] := true; d[1] := s; {队列的初始状态,s为起点}
  head := 1; tail := 1;
  while head<=tail do {队列不空}
    begin
      now := d[head]; {取队首元素}
      for i := 1 to b[now,0] do
        if dist[b[now,i]]>dist[now]+a[now,b[now,i]] then
          begin
            dist[b[now,i]]:= dist[now]+a[now,b[now,i]]; {修改最短路}
            if not v[b[now,i]] then {扩展结点入队}
              begin
                inc(tail);
                d[tail] := b[now,i];
                v[b[now,i]] := true;
              end;
          end;
      v[now] := false; {释放结点}
      inc(head); {出队}
    end;
end;
procedure print;
begin
  writeln(dist[t]);
end;
begin
  init;
  spfa(s);
  print;
end.