bellman-ford算法模板

var
  e:array[1..maxe]of record a,b,w:longint;end;
  { 距源点s距离 }
  dis:array[1..maxn]of longint;
  { 前驱 }
  pre:array[1..maxn]of longint;
  m,n,s:longint;
procedure relax(u,v,w:longint);
  begin
    if dis[u]+w<dis[v] then
      begin
        dis[v]:=dis[u]+w;
        pre[v]:=u;
      end;
  end;
function bellman_ford:boolean;
  var i,j:longint;
  begin
    { 每条边松弛 }
    for i:=1 to n-1 do
      for j:=1 to m do
        with e[j] do
          relax(a,b,w);
    { 如果还能松弛 }
    for i:=1 to m do
      with e[i] do
        if dis[a]+w<dis[b] then
          exit(false);
    exit(true)
  end;