bzoj1690:[Usaco2007 Dec]奶牛的旅行（分数规划+spfa判负环）

type
  point=^rec;
  rec=record
    data:longint;
    sum:extended;
    next:point;
  end;
var
  n,m,x,y,z,i:longint;
  k:point;
  l,r,mid:extended;
  dist:array[0..1000]of extended;
  h:array[0..10000000]of longint;
  fun,num:array[0..1000]of longint;
  v:array[0..1000]of boolean;
  map:array[0..1000]of point;

function spfa(x:longint):boolean;
var
  front,rear,now,j:longint;
  sum:extended;
  i:point;
begin
  for j:=1 to n do dist[j]:=maxlongint;
  dist[x]:=0;front:=0;rear:=1;h[1]:=x;v[x]:=true;
  while front<rear do
  begin
    inc(front);
    now:=h[front];
    i:=map[now];
    while i<>nil do
    begin
      sum:=i^.sum*mid-fun[i^.data];
      if dist[i^.data]>dist[now]+sum then
      begin
        dist[i^.data]:=dist[now]+sum;
        if not v[i^.data] then
        begin
          if num[i^.data]>233 then exit(true);
          inc(rear);
          inc(num[i^.data]);
          h[rear]:=i^.data;
          v[i^.data]:=true;
        end;
      end;
      i:=i^.next;
    end;
    v[now]:=false;
  end;
  exit(false);
end;

begin
  readln(n,m);
  for i:=1 to n do read(fun[i]);
  for i:=1 to m do
  begin
    readln(x,y,z);
    new(k);
    k^.data:=y;
    k^.sum:=z;
    k^.next:=map[x];
    map[x]:=k;
  end;
  l:=0;r:=10000;
  while (r-l>0.001) do
  begin
    fillchar(v,sizeof(v),false);
    fillchar(num,sizeof(num),0);
    mid:=(l+r)/2;
    if spfa(1) then l:=mid
    else r:=mid;
  end;
  writeln(l:0:2);
end.