#include "bits/stdc++.h" // Tomasz Nowak
using namespace std; // XIII LO Szczecin
using LL = long long; // Poland
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
template<class T> int size(T &&x) {
return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
out << '{';
for(auto it = x.begin(); it != x.end(); ++it)
out << *it << (it == prev(x.end()) ? "" : ", ");
return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
cerr << x << "; ";
dump(args...);
}
#ifdef DEBUG
struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ": " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
mt19937_64 rng(0);
int rd(int l, int r) {
return uniform_int_distribution<int>(l, r)(rng);
}
// end of templates
vector<pair<int, int>> edges;
vector<vector<int>> graph;
vector<bool> blocked_edge;
int to(int v, int e) {
return edges[e].first ^ edges[e].second ^ v;
}
vector<int> pre, low;
vector<int> parent_edge;
int gtime = 0;
void dfs(int v, int par_edge = -1) {
pre[v] = low[v] = gtime++;
parent_edge[v] = par_edge;
for(int e : graph[v])
if(not blocked_edge[e] and e != par_edge) {
int u = to(v, e);
if(pre[u] == -1) {
dfs(u, e);
low[v] = min(low[v], low[u]);
}
else if(pre[u] < pre[v])
low[v] = min(low[v], pre[u]);
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, m;
cin >> n >> m;
edges.resize(m);
graph.resize(n);
REP(i, m) {
auto &[v, u] = edges[i];
cin >> v >> u;
--v, --u;
graph[v].emplace_back(i);
graph[u].emplace_back(i);
}
LL ans = 0;
REP(e1, m)
REP(e2, e1) {
pre.assign(n, -1);
gtime = 0;
low = pre;
blocked_edge.assign(m, false);
blocked_edge[e1] = blocked_edge[e2] = true;
parent_edge.assign(n, -1);
dfs(0);
// debug(e1, e2, pre, low, parent_edge);
if(*min_element(pre.begin(), pre.end()) == -1) {
ans += m - 2;
continue;
}
int bridges = 0;
REP(v, n)
if(parent_edge[v] != -1) {
int u = to(v, parent_edge[v]);
if(pre[u] < low[v])
++bridges;
}
debug(e1, e2, bridges);
ans += bridges;
}
cout << (ans / 3) << '\n';
}
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 97 98 99 100 101 102 103 104 | #include "bits/stdc++.h" // Tomasz Nowak using namespace std; // XIII LO Szczecin using LL = long long; // Poland #define FOR(i, l, r) for(int i = (l); i <= (r); ++i) #define REP(i, n) FOR(i, 0, (n) - 1) template<class T> int size(T &&x) { return int(x.size()); } template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) { return out << '(' << p.first << ", " << p.second << ')'; } template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) { out << '{'; for(auto it = x.begin(); it != x.end(); ++it) out << *it << (it == prev(x.end()) ? "" : ", "); return out << '}'; } void dump() {} template<class T, class... Args> void dump(T &&x, Args... args) { cerr << x << "; "; dump(args...); } #ifdef DEBUG struct Nl{~Nl(){cerr << '\n';}}; # define debug(x...) cerr << (strcmp(#x, "") ? #x ": " : ""), dump(x), Nl(), cerr << "" #else # define debug(...) 0 && cerr #endif mt19937_64 rng(0); int rd(int l, int r) { return uniform_int_distribution<int>(l, r)(rng); } // end of templates vector<pair<int, int>> edges; vector<vector<int>> graph; vector<bool> blocked_edge; int to(int v, int e) { return edges[e].first ^ edges[e].second ^ v; } vector<int> pre, low; vector<int> parent_edge; int gtime = 0; void dfs(int v, int par_edge = -1) { pre[v] = low[v] = gtime++; parent_edge[v] = par_edge; for(int e : graph[v]) if(not blocked_edge[e] and e != par_edge) { int u = to(v, e); if(pre[u] == -1) { dfs(u, e); low[v] = min(low[v], low[u]); } else if(pre[u] < pre[v]) low[v] = min(low[v], pre[u]); } } int main() { ios_base::sync_with_stdio(0); cin.tie(0); int n, m; cin >> n >> m; edges.resize(m); graph.resize(n); REP(i, m) { auto &[v, u] = edges[i]; cin >> v >> u; --v, --u; graph[v].emplace_back(i); graph[u].emplace_back(i); } LL ans = 0; REP(e1, m) REP(e2, e1) { pre.assign(n, -1); gtime = 0; low = pre; blocked_edge.assign(m, false); blocked_edge[e1] = blocked_edge[e2] = true; parent_edge.assign(n, -1); dfs(0); // debug(e1, e2, pre, low, parent_edge); if(*min_element(pre.begin(), pre.end()) == -1) { ans += m - 2; continue; } int bridges = 0; REP(v, n) if(parent_edge[v] != -1) { int u = to(v, parent_edge[v]); if(pre[u] < low[v]) ++bridges; } debug(e1, e2, bridges); ans += bridges; } cout << (ans / 3) << '\n'; } |
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