const inf=maxlongint shr 1;
type alice=record
x,y,f,next,op:longint;
end;
var tot,n,m,s,t,i,head,tail,sum,ii,iii:longint;
first,tfirst:array[1..1000]of longint;
bian:array[1..100000]of alice;
level,xx,yy,ff,q,u,r:array[1..10000]of longint;
v:array[1..1000]of boolean;
g:array[1..1000,1..1000]of boolean;
procedure connect(x,y,f:Longint);
begin
inc(tot);
bian[tot].x:=x;
bian[tot].y:=y;
bian[tot].f:=f;
bian[tot].op:=tot+1;
bian[tot].next:=first[x];
first[x]:=tot;
inc(tot);
bian[tot].x:=y;
bian[tot].y:=x;
bian[tot].f:=f;
bian[tot].op:=tot-1;
bian[tot].next:=first[y];
first[y]:=tot;
end;
function bfs:boolean;
var j,k,x,y:longint;
begin
for j:=1 to n do
begin
level[j]:=inf;
v[j]:=false;
tfirst[j]:=first[j];
end;
head:=0;
tail:=1;
q[1]:=s;
level[s]:=0;
v[s]:=true;
repeat
inc(head);
x:=q[head];
k:=first[x];
while k<>0 do
begin
y:=bian[k].y;
if bian[k].f>0 then
if level[y]>level[x]+1 then
begin
level[y]:=level[x]+1;
if not v[y] then
begin
inc(tail);
q[tail]:=y;
v[y]:=true;
if y=t then exit(true);
end;
end;
k:=bian[k].next;
end;
v[x]:=false;
until head=tail;
exit(false);
end;
function min(a,b:longint):longint;
begin
if a<b then exit(a)
else exit(b);
end;
function dfs(x,ff:longint):longint;
var y,j,k,tf,tmp:longint;
begin
if x=t then exit(ff);
tf:=0;
k:=tfirst[x];
while k<>0 do
begin
tfirst[x]:=k;
y:=bian[k].y;
if bian[k].f>0 then
if level[y]=level[x]+1 then
begin
tmp:=dfs(y,min(ff,bian[k].f));
if tmp>0 then
begin
dec(bian[k].f,tmp);
inc(tf,tmp);
inc(bian[bian[k].op].f,tmp);
dec(ff,tmp);
end;
end;
k:=bian[k].next;
end;
exit(tf);
end;
procedure main;
var tmp:longint;
begin
while bfs do
begin
tmp:=dfs(s,inf);
while tmp>0 do tmp:=dfs(s,inf);
end;
end;
begin
readln(n,m,s,t);
for i:=1 to m do
begin
readln(xx[i],yy[i],ff[i]);
connect(xx[i],yy[i],ff[i]);
u[i]:=tot-1;
end;
main;//找最大流
fillchar(g,sizeof(g),false);
for i:=1 to n do
begin
ii:=first[i];
while ii<>0 do
begin
if bian[ii].f>0 then g[i,bian[ii].y]:=true;
ii:=bian[ii].next;
end;
end;
for i:=1 to n do //传递闭包
for ii:=1 to n do
for iii:=1 to n do
g[i,ii]:=g[i,ii] or(g[i,iii] and g[iii,ii]);
sum:=0;
for i:=1 to m do
if (not g[xx[i],yy[i]])or(not g[yy[i],xx[i]]) then
begin
inc(sum);
r[sum]:=i;
end;
writeln(sum);
for i:=1 to sum do writeln(r[i]);
end.
dinic后用残量网络传递闭包
（学的时间不长，很多术语都不懂，所以没写多少注释……大家将就着看程序吧）