#include <bits/stdc++.h> using namespace std; typedef long long int LL; const int MAXN = 200005; const int MAXE = 500005; unordered_set<int> blocked_edges; int n, m; vector<pair<int,int>> adj[MAXN]; vector<pair<int,int>> edges; bool visited[MAXN]; bool bridge[MAXE]; int low[MAXN], dist[MAXN], parent[MAXN], cnt_visited; void dfs(int u) { visited[u] = true; low[u] = dist[u]; cnt_visited++; unordered_map<int,int> cnt_edges; vector<bool> dfs_edges(adj[u].size(), false); for (int i = 0; i < adj[u].size(); i++) { const auto& e = adj[u][i]; int v = e.first; int eid = e.second; if (v == parent[u]) continue; if (blocked_edges.count(eid)) continue; cnt_edges[v]++; if (!visited[v]) { dist[v] = dist[u] + 1; parent[v] = u; dfs(v); low[u] = min(low[u], low[v]); dfs_edges[i] = true; } else low[u] = min(low[u], dist[v]); } for (int i = 0; i < adj[u].size(); i++) { if (!dfs_edges[i]) continue; const auto& e = adj[u][i]; int v = e.first; int eid = e.second; if ((cnt_edges[v] == 1) && (low[v] == dist[v])) bridge[eid] = true; } } int run_low(int min_eid) { fill(visited, visited+n, false); fill(bridge, bridge+m, false); cnt_visited = 0; dist[0] = 0; parent[0] = -1; dfs(0); if (cnt_visited < n) return m - min_eid; int r = 0; for (int eid = min_eid; eid < m; eid++) if (bridge[eid]) r++; return r; } int main() { ios_base::sync_with_stdio(false); cin.tie(0); cin >> n >> m; for (int i = 0; i < m; i++) { int u, v; cin >> u >> v; u--; v--; adj[u].push_back(make_pair(v, i)); adj[v].push_back(make_pair(u, i)); edges.push_back(make_pair(u, v)); } LL result = 0; for (int i = 0; i < m; i++) { blocked_edges.insert(i); for (int j = i+1; j < m; j++) { blocked_edges.insert(j); result += run_low(j+1); blocked_edges.erase(j); } blocked_edges.erase(i); } cout << result << "\n"; return 0; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 | #include <bits/stdc++.h> using namespace std; typedef long long int LL; const int MAXN = 200005; const int MAXE = 500005; unordered_set<int> blocked_edges; int n, m; vector<pair<int,int>> adj[MAXN]; vector<pair<int,int>> edges; bool visited[MAXN]; bool bridge[MAXE]; int low[MAXN], dist[MAXN], parent[MAXN], cnt_visited; void dfs(int u) { visited[u] = true; low[u] = dist[u]; cnt_visited++; unordered_map<int,int> cnt_edges; vector<bool> dfs_edges(adj[u].size(), false); for (int i = 0; i < adj[u].size(); i++) { const auto& e = adj[u][i]; int v = e.first; int eid = e.second; if (v == parent[u]) continue; if (blocked_edges.count(eid)) continue; cnt_edges[v]++; if (!visited[v]) { dist[v] = dist[u] + 1; parent[v] = u; dfs(v); low[u] = min(low[u], low[v]); dfs_edges[i] = true; } else low[u] = min(low[u], dist[v]); } for (int i = 0; i < adj[u].size(); i++) { if (!dfs_edges[i]) continue; const auto& e = adj[u][i]; int v = e.first; int eid = e.second; if ((cnt_edges[v] == 1) && (low[v] == dist[v])) bridge[eid] = true; } } int run_low(int min_eid) { fill(visited, visited+n, false); fill(bridge, bridge+m, false); cnt_visited = 0; dist[0] = 0; parent[0] = -1; dfs(0); if (cnt_visited < n) return m - min_eid; int r = 0; for (int eid = min_eid; eid < m; eid++) if (bridge[eid]) r++; return r; } int main() { ios_base::sync_with_stdio(false); cin.tie(0); cin >> n >> m; for (int i = 0; i < m; i++) { int u, v; cin >> u >> v; u--; v--; adj[u].push_back(make_pair(v, i)); adj[v].push_back(make_pair(u, i)); edges.push_back(make_pair(u, v)); } LL result = 0; for (int i = 0; i < m; i++) { blocked_edges.insert(i); for (int j = i+1; j < m; j++) { blocked_edges.insert(j); result += run_low(j+1); blocked_edges.erase(j); } blocked_edges.erase(i); } cout << result << "\n"; return 0; } |