二分图的（不）可行边。
#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
#include <queue>
using namespace std;
int n, m, T, ss, tt, hea[20005], cnt, uu[100005], vv[100005], cur[20005], scc;
int lev[20005], dfn[20005], bel[20005], idx, loo[20005], sta[20005], din, maxFlow;
int oea[20005], ont;
bool ins[20005];
const int oo=0x3f3f3f3f;
queue<int> d;
vector<int> vec;
struct Edge{
int too, nxt, val;
}edge[300005], odge[300005];
void add_edge(int fro, int too, int val){
edge[cnt].nxt = hea[fro];
edge[cnt].too = too;
edge[cnt].val = val;
hea[fro] = cnt++;
}
void addEdge(int fro, int too){
add_edge(fro, too, 1);
add_edge(too, fro, 0);
}
void add_odge(int fro, int too){
odge[++ont].nxt = oea[fro];
odge[ont].too = too;
oea[fro] = ont;
}
bool bfs(){
memset(lev, 0, sizeof(lev));
lev[ss] = 1;
d.push(ss);
while(!d.empty()){
int x=d.front();
d.pop();
for(int i=hea[x]; i!=-1; i=edge[i].nxt){
int t=edge[i].too;
if(!lev[t] && edge[i].val>0){
lev[t] = lev[x] + 1;
d.push(t);
}
}
}
return lev[tt]!=0;
}
int dfs(int x, int lim){
if(x==tt) return lim;
int addFlow=0;
for(int &i=cur[x]; i!=-1; i=edge[i].nxt){
int t=edge[i].too;
if(lev[t]==lev[x]+1 && edge[i].val>0){
int tmp=dfs(t, min(lim-addFlow, edge[i].val));
edge[i].val -= tmp;
edge[i^1].val += tmp;
addFlow += tmp;
if(addFlow==lim) break;
}
}
return addFlow;
}
void dinic(){
while(bfs()){
for(int i=ss; i<=tt; i++) cur[i] = hea[i];
maxFlow += dfs(ss, oo);
}
}
void tarjan(int x){
dfn[x] = loo[x] = ++idx;
ins[x] = true;
sta[++din] = x;
for(int i=oea[x]; i; i=odge[i].nxt){
int t=odge[i].too;
if(!dfn[t]){
tarjan(t);
loo[x] = min(loo[x], loo[t]);
}
else if(ins[t]) loo[x] = min(loo[x], dfn[t]);
}
int j;
if(dfn[x]==loo[x]){
scc++;
do{
j = sta[din--];
ins[j] = false;
bel[j] = scc;
}while(dfn[j]!=loo[j]);
}
}
int main(){
memset(hea, -1, sizeof(hea));
cin>>n>>m>>T;
for(int i=1; i<=T; i++){
scanf("%d %d", &uu[i], &vv[i]);
addEdge(uu[i], n+vv[i]);
}
ss = 0; tt = n + m + 1;
for(int i=1; i<=n; i++)
addEdge(ss, i);
for(int i=1; i<=m; i++)
addEdge(n+i, tt);
dinic();
for(int i=ss; i<=tt; i++){
for(int j=hea[i]; j!=-1; j=edge[j].nxt){
if(j&1) continue;
if(!edge[j].val) add_odge(edge[j].too, i);
else add_odge(i, edge[j].too);
}
}
for(int i=ss; i<=tt; i++)
if(!dfn[i])
tarjan(i);
for(int i=1; i<=T; i++){
if(edge[2*i-1].val) continue;
if(bel[uu[i]]==bel[vv[i]+n]) continue;
vec.push_back(i);
}
cout<<vec.size()<<endl;
if(!vec.size()){
cout<<endl;
return 0;
}
for(int i=0; i<vec.size()-1; i++)
printf("%d ", vec[i]);
cout<<vec[vec.size()-1]<<endl;
return 0;
}