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Codeforces Round 1043 (Div. 3)/F. Rada and the Chamomile Valley.cpp

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+/* Problem URL: https://codeforces.com/contest/2132/problem/F */
+
+#include <bits/stdc++.h>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/tree_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+template <class T, class comp = less<>>
+using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
+
+#define V vector
+
+#define rmin(a, b) a = min(a, b)
+#define rmax(a, b) a = max(a, b)
+
+#define rep(i, lim) for (int i = 0; i < (lim); i++)
+#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
+
+#define repv(i, v) for (auto &i : (v))
+#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
+#define sortv(v) sort(v.begin(), v.end())
+#define all(v) (v).begin(), (v).end()
+
+using vi = vector<int>;
+using vvi = vector<vi>;
+using vvvi = vector<vvi>;
+using vvvvi = vector<vvvi>;
+
+using ll = long long;
+
+using vl = vector<ll>;
+using vvl = vector<vl>;
+using vvvl = vector<vvl>;
+using vvvvl = vector<vvvl>;
+
+template<class v>
+auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
+    os << vec[0];
+    for (size_t i = 1; i < vec.size(); i++) {
+        os << ' ' << vec[i];
+    }
+    os << '\n';
+    return os;
+}
+
+template<class v>
+auto operator>>(istream &is, vector<v> &vec)->istream& {
+    for (auto &i : vec) {
+        is >> i;
+    }
+    return is;
+}
+
+template<class v>
+auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
+    for (auto &i : vec) {
+        os << i[0];
+        for (size_t j = 1; j < i.size(); j++) {
+            os << ' ' << i[j];
+        }
+        os << '\n';
+    }
+    return os;
+}
+
+template<class v>
+auto operator>>(istream  &is, vector<vector<v>> &vec)->istream& {
+    for (auto &i : vec) {
+        for (auto &j : i) {
+            is >> j;
+        }
+    }
+    return is;
+}
+
+int main()
+{
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int t;
+    cin >> t;
+    while (t--) {
+        int n, m;
+        cin >> n >> m;
+
+        V<V<pair<int, int>>> graph(n);
+
+        rep(i, m) {
+            int a, b;
+            cin >> a >> b;
+            a--, b--;
+
+            graph[a].emplace_back(b, i);
+            graph[b].emplace_back(a, i);
+        }
+
+        V<V<pair<int, int>>> tree(n);
+
+        int inf = INT32_MAX >> 1;
+
+        int t = 0;
+        vi low(n, inf);
+        vi time(n, inf);
+        V<bool> vis(n);
+        V<bool> bridge(m);
+        vi ans(n, inf);
+
+        function<void(int, int)> dfs = [&](int i, int p) {
+            low[i] = t;
+            time[i] = t;
+            t++;
+
+            vis[i] = true;
+
+            for (auto [j, id] : graph[i]) {
+                if (j == p) {
+                    continue;
+                }
+
+                if (vis[j]) {
+                    rmin(low[i], time[j]);
+                    continue;
+                }
+
+                dfs(j, i);
+                tree[i].emplace_back(j, id);
+                rmin(low[i], low[j]);
+
+                if (low[j] > time[i]) {
+                    bridge[id] = true;
+                }
+            }
+        };
+
+        dfs(0, -1);
+
+        vi tmp;
+
+        function<bool(int)> search = [&](int i) {
+            if (i == n - 1) {
+                return true;
+            }
+
+            for (auto [j, id] : tree[i]) {
+                if (search(j)) {
+                    if (bridge[id]) {
+                        tmp.push_back(i);
+                        tmp.push_back(j);
+                        rmin(ans[i], id);
+                        rmin(ans[j], id);
+                    }
+
+                    return true;
+                }
+            }
+
+            return false;
+        };
+
+        search(0);
+
+        set<pair<int, int>> fds;
+        repv(i, tmp) {
+            fds.emplace(ans[i], i);
+        }
+
+        int q;
+        cin >> q;
+
+        if (tmp.empty()) {
+            while (q--) {
+                int t;
+                cin >> t;
+                cout << "-1 ";
+            }
+            cout << '\n';
+
+            continue;
+        }
+
+
+        auto getans = [&]() {
+            queue<int> q;
+            vi level(n, inf);
+
+            for (auto [id, i] : fds) {
+                q.push(i);
+                level[i] = 0;
+            }
+
+            while (!q.empty()) {
+                int i = q.front();
+                q.pop();
+
+                for (auto [j, id] : graph[i]) {
+                    if (level[j] > level[i] + 1) {
+                        level[j] = level[i] + 1;
+                        ans[j] = ans[i];
+                        q.push(j);
+                        continue;
+                    }
+
+                    if (level[j] == level[i] + 1) {
+                        rmin(ans[j], ans[i]);
+                    }
+                }
+            }
+        };
+
+        getans();
+
+        while (q--) {
+            int x;
+            cin >> x;
+
+            cout << ans[x - 1] + 1 << ' ';
+        }
+        cout << '\n';
+    }
+}