Reverse Roads http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=2304

aoj2304.cpp

#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define rrep2(i,a,b) for (int i=(a)-1;i>=b;i--)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define printV(_v) for(auto _x:_v){cout<<_x<<" ";}cout<<endl
#define printVS(_vs) for(auto _x : _vs){cout << _x << endl;}
#define printVV(_vv) for(auto _v:_vv){for(auto _x:_v){cout<<_x<<" ";}cout<<endl;}
#define printP(_p) cout << _p.first << " " << _p.second << endl
#define printVP(_vp) for(auto _p : _vp) printP(_p);

typedef long long ll;
typedef pair<int, int> Pii;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vector<int>> Graph;
const int inf = 1e9;
const int mod = 1e9 + 7;

struct edge { int to, cap, rev; };

const int MAX_V = 300;
vector<edge> G[MAX_V];
int level[MAX_V];
int iter[MAX_V];

void add_edge(int from, int to, int cap) {
    G[from].emplace_back((edge){to, cap, (int)G[to].size()});
    G[to].emplace_back((edge){from, 0, (int)G[from].size() - 1});
}

void bfs(int s) {
    memset(level, -1, sizeof(level));
    queue<int> que;
    level[s] = 0;
    que.push(s);
    while (!que.empty()) {
        int v = que.front(); que.pop();
        for (int i = 0; i < G[v].size(); i++) {
            edge &e = G[v][i];
            if (e.cap > 0 && level[e.to] < 0) {
                level[e.to] = level[v] + 1;
                que.push(e.to);
            }
        }
    }
}

int dfs(int v, int t, int f) {
    if (v == t) return f;
    for (int &i = iter[v]; i < G[v].size(); i++) {
        edge &e = G[v][i];
        if (e.cap > 0 && level[v] < level[e.to]) {
            int d = dfs(e.to, t, min(f, e.cap));
            if (d > 0) {
                e.cap -= d;
                G[e.to][e.rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}

int max_flow(int s, int t) {
    int flow = 0;
    for (;;) {
        bfs(s);
        if (level[t] < 0) return flow;
        memset(iter, 0, sizeof(iter));
        int f;
        while ((f = dfs(s, t, inf)) > 0) {
            flow += f;
        }
    }
}


signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int n, m;
    cin >> n >> m;
    map<Pii, int> mp;
    rep(i, m) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        mp[Pii(a, b)] = i;
        add_edge(a, b, 1);
        add_edge(b, a, 1);
    }
    int s, t;
    cin >> s >> t;
    s--; t--;

    int F = max_flow(s, t);
    int R = 0;
    set<int> st;
    rep(i, n) {
        for (auto e : G[i]) {
            if (mp.count(Pii(i, e.to)) && e.cap != 0 && G[e.to][e.rev].cap == 0 && !st.count(mp[Pii(i, e.to)])) {
                R++;
                st.insert(mp[Pii(i, e.to)]);
            }
        }
    }

    cout << F << endl;
    cout << R << endl;
    for (auto i : st) {
        cout << i + 1 << endl;
    }

}