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  1. #include <bits/stdc++.h>
  2. #define ll long long
  3. #define INF 1000000005
  4. #define MOD 1000000007
  5. #define EPS 1e-10
  6. #define rep(i,n) for(int i=0;i<(int)(n);++i)
  7. #define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
  8. #define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
  9. #define each(a,b) for(auto& (a): (b))
  10. #define all(v) (v).begin(),(v).end()
  11. #define len(v) (int)(v).size()
  12. #define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
  13. #define cmx(x,y) x=max(x,y)
  14. #define cmn(x,y) x=min(x,y)
  15. #define fi first
  16. #define se second
  17. #define pb push_back
  18. #define show(x) cout<<#x<<" = "<<(x)<<endl
  19. #define sar(a,n) {cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl;}
  20.  
  21. using namespace std;
  22.  
  23. template<typename S,typename T>auto&operator<<(ostream&o,pair<S,T>p){return o<<"{"<<p.fi<<","<<p.se<<"}";}
  24. template<typename T>auto&operator<<(ostream&o,set<T>s){for(auto&e:s)o<<e<<" ";return o;}
  25. template<typename S,typename T,typename U>
  26. auto&operator<<(ostream&o,priority_queue<S,T,U>q){while(!q.empty())o<<q.top()<<" ",q.pop();return o;}
  27. template<typename K,typename T>auto&operator<<(ostream&o,map<K,T>&m){for(auto&e:m)o<<e<<" ";return o;}
  28. template<typename T>auto&operator<<(ostream&o,vector<T>v){for(auto&e:v)o<<e<<" ";return o;}
  29. void ashow(){cout<<endl;}template<typename T,typename...A>void ashow(T t,A...a){cout<<t<<" ";ashow(a...);}
  30. template<typename S,typename T,typename U>
  31. struct TRI{S fi;T se;U th;TRI(){}TRI(S f,T s,U t):fi(f),se(s),th(t){}
  32. bool operator<(const TRI&_)const{return(fi==_.fi)?((se==_.se)?(th<_.th):(se<_.se)):(fi<_.fi);}};
  33. template<typename S,typename T,typename U>
  34. auto&operator<<(ostream&o,TRI<S,T,U>&t){return o<<"{"<<t.fi<<","<<t.se<<","<<t.th<<"}";}
  35.  
  36. typedef pair<int, int> P;
  37. typedef pair<ll, ll> pll;
  38. typedef TRI<int, int, int> tri;
  39. typedef vector<int> vi;
  40. typedef vector<ll> vl;
  41. typedef vector<vi> vvi;
  42. typedef vector<vl> vvl;
  43. typedef vector<P> vp;
  44. typedef vector<double> vd;
  45. typedef vector<string> vs;
  46.  
  47. const int MAX_N = 100005;
  48.  
  49. class FindingAllCycles {
  50. private:
  51.     struct node {
  52.         int prev, next, to;
  53.         node(const int _prev, const int _next, const int _to)
  54.             : prev(_prev), next(_next), to(_to){}
  55.     };
  56.     const int V;
  57.     vector<vector<node> > G;
  58.     vector<stack<int> > block_stack;
  59.     stack<int> st;
  60.     bool *fix, *blocked, *used;
  61.     bool enumerate;
  62.     void erase_edge(const int u, const int id){
  63.         G[u][G[u][id].next].prev = G[u][id].prev;
  64.         G[u][G[u][id].prev].next = G[u][id].next;
  65.     }
  66.     void scc_dfs(const int u, int& tm, int& cnt,
  67.             vector<int>& ord, vector<int>& low, vector<int>& cmp, stack<int>& st){
  68.         ord[u] = low[u] = tm++, st.push(u);
  69.         for(int id = G[u][0].next; id != 0; id = G[u][id].next){
  70.             const int v = G[u][id].to;
  71.             if(ord[v] < 0){
  72.                 scc_dfs(v, tm, cnt, ord, low, cmp, st);
  73.                 low[u] = min(low[u], low[v]);
  74.             }else if(cmp[v] < 0){
  75.                 low[u] = min(low[u], ord[v]);
  76.             }
  77.             if(cmp[v] >= 0) erase_edge(u, id);
  78.         }
  79.         if(ord[u] == low[u]){
  80.             while(true){
  81.                 const int v = st.top();
  82.                 st.pop(), cmp[v] = cnt;
  83.                 if(v == u) break;
  84.             }
  85.             ++cnt;
  86.         }
  87.     }
  88.     void scc(){
  89.         vector<int> ord(V, -1), low(V), cmp(V, -1);
  90.         stack<int> st;
  91.         int tm = 0, cnt = 0;
  92.         for(int i = 0; i < V; ++i){
  93.             if(ord[i] < 0) scc_dfs(i, tm, cnt, ord, low, cmp, st);
  94.         }
  95.     }
  96.     void unblock(const int u){
  97.         blocked[u] = false;
  98.         while(!block_stack[u].empty()){
  99.             const int v = block_stack[u].top();
  100.             block_stack[u].pop();
  101.             if(blocked[v]) unblock(v);
  102.         }
  103.     }
  104.     bool dfs(const int u, const int s, vector<int>& path, vector<int>& ver_list){
  105.         bool flag = false;
  106.         path.push_back(u);
  107.         blocked[u] = true;
  108.         if(!used[u]) used[u] = true, ver_list.push_back(u);
  109.         for(int id = G[u][0].next; id != 0; id = G[u][id].next){
  110.             const int v = G[u][id].to;
  111.             if(fix[v]){
  112.                 erase_edge(u, id);
  113.                 continue;
  114.             }
  115.             if(v == s){
  116.                 if(enumerate) ans.push_back(path);
  117.                 ++count, flag = true;
  118.             }else if(!blocked[v]){
  119.                 if(dfs(v, s, path, ver_list)) flag = true;
  120.             }
  121.         }
  122.         if(flag) unblock(u);
  123.         else{
  124.             for(int id = G[u][0].next; id != 0; id = G[u][id].next){
  125.                 block_stack[G[u][id].to].push(u);
  126.             }
  127.         }
  128.         path.pop_back();
  129.         return flag;
  130.     }
  131.  
  132. public:
  133.     vector<vector<int> > ans;
  134.     int count;
  135.     FindingAllCycles(const int node_size)
  136.         : V(node_size), G(V, vector<node>{{0, 0, -1}}), block_stack(V),
  137.             fix(new bool[V]()), blocked(new bool[V]()), used(new bool[V]()), count(0){}
  138.     ~FindingAllCycles(){
  139.         delete[] fix, delete[] blocked, delete[] used;
  140.     }
  141.     void add_edge(const int u, const int v){
  142.         if(u == v){
  143.             ans.push_back({u});
  144.             return;
  145.         }
  146.         G[u][0].prev = G[u].back().next = (int)G[u].size();
  147.         G[u].push_back((node){(int)G[u].size() - 1, 0, v});
  148.     }
  149.     int solve(bool _enumerate=true){
  150.         scc();
  151.         enumerate = _enumerate;
  152.         for(int i = 0; i < V; ++i){
  153.             vector<int> path, ver_list;
  154.             dfs(i, i, path, ver_list);
  155.             fix[i] = true;
  156.             for(int j : ver_list){
  157.                 used[j] = blocked[j] = false, block_stack[j] = stack<int>();
  158.             }
  159.         }
  160.         return count;
  161.     }
  162. };
  163.  
  164. template<typename T> class segtree {
  165. private:
  166.     int n,sz;
  167.     vector<pair<T, int> > node;
  168. public:
  169.     void resize(vector<T>& v){
  170.         sz = (int)v.size();
  171.         n = 1;
  172.         while(n < sz){
  173.             n *= 2;
  174.         }
  175.         node.resize(2*n);
  176.         for(int i = 0; i < sz; i++){
  177.             node[i+n] = make_pair(v[i], i);
  178.         }
  179.         for(int i=n-1; i>=1; i--){
  180.             node[i] = min(node[2*i], node[2*i+1]);
  181.         }
  182.     }
  183.     void update(int k, T a)
  184.     {
  185.     	node[k+=n] = make_pair(a, k);
  186.     	while(k>>=1){
  187.             node[k] = min(node[2*k], node[2*k+1]);
  188.     	}
  189.     }
  190.     pair<T, int> query(int a,int b)
  191.     {
  192.         pair<T, int> res1 = make_pair(numeric_limits<T>::max(), -1);
  193.         pair<T, int> res2 = make_pair(numeric_limits<T>::max(), -1);
  194.         a += n, b += n;
  195.         while(a != b){
  196.             if(a % 2) res1 = min(res1, node[a++]);
  197.             if(b % 2) res2 = min(res2, node[--b]);
  198.             a >>= 1, b >>= 1;
  199.         }
  200.         return min(res1, res2);
  201.     }
  202. };
  203.  
  204. struct edge {
  205.     int from, to, id;
  206.     edge(const int _from, const int _to, const int _id)
  207.         : from(_from), to(_to), id(_id){}
  208. };
  209.  
  210. class LCA{
  211. public:
  212.     int V;
  213.     vector<vector<int> > G;
  214.     vector<int> ord,depth,id;
  215.     segtree<int> st;
  216.     LCA(int node_size) : V(node_size), G(V), depth(V), id(V, -1){}
  217.     void add_edge(int from,int to){
  218.         G[from].push_back(to),G[to].push_back(from);
  219.     }
  220.     void dfs(int u,int p,int k){
  221.         id[u] = (int)ord.size();
  222.         ord.push_back(u);
  223.         depth[u] = k;
  224.         for(int v : G[u]){
  225.             if(v != p){
  226.                 dfs(v,u,k+1);
  227.                 ord.push_back(u);
  228.             }
  229.         }
  230.     }
  231.     void build(){
  232.         ord.reserve(2*V-2);
  233.         for(int i = 0; i < V; i++){
  234.             if(id[i] < 0){
  235.                 dfs(i,-1,0);
  236.             }
  237.         }
  238.         vector<int> stvec(2*V-2);
  239.     	for(int i = 0; i < 2*V-2; i++){
  240.     		stvec[i] = depth[ord[i]];
  241.     	}
  242.         st.resize(stvec);
  243.     }
  244.     int solve(int u,int v){
  245.         return ord[st.query(min(id[u],id[v]),max(id[u],id[v])+1).second];
  246.     }
  247.     int dist(int u,int v){
  248.         int lca = solve(u,v);
  249.         return depth[u] + depth[v] - 2*depth[lca];
  250.     }
  251.     pair<int, int> construct_virtual_tree(vector<int>& ver_list, unordered_map<int, int>& mapping);
  252. };
  253.  
  254. vector<pair<int, int> > es;
  255.  
  256. pair<int, int> LCA::construct_virtual_tree(vector<int>& ver_list, unordered_map<int, int>& mapping){
  257.     const int n = (int)ver_list.size();
  258.     sort(ver_list.begin(), ver_list.end(), [&](const int a, const int b){
  259.         return id[a] < id[b];
  260.     });
  261.     stack<int> st;
  262.     st.push(ver_list[0]), mapping[ver_list[0]] = 0;
  263.     int id = n;
  264.     for(int i = 0; i < n-1; ++i){
  265.         const int u = solve(ver_list[i], ver_list[i+1]);
  266.         if(u != ver_list[i]){
  267.             int mapped_ver = mapping[st.top()];
  268.             while(true){
  269.                 st.pop();
  270.                 if(st.empty() || depth[u] >= depth[st.top()]) break;
  271.                 const int tmp = mapping[st.top()];
  272.                 es.push_back({tmp, mapped_ver});
  273.                 mapped_ver = tmp; 
  274.             }
  275.             if(st.empty() || st.top() != u){
  276.                 st.push(u), ver_list.push_back(u);
  277.                 es.push_back({id, mapped_ver});
  278.                 mapping[u] = id++;
  279.             }else{
  280.                 es.push_back({mapping[u], mapped_ver});
  281.             }
  282.         }
  283.         st.push(ver_list[i+1]), mapping[ver_list[i+1]] = i+1;
  284.     }
  285.     int mapped_ver = ((st.size() > 1) ? mapping[st.top()] : -1);
  286.     while(st.size() > 1){
  287.         st.pop();
  288.         const int tmp = mapping[st.top()];
  289.         es.push_back({tmp, mapped_ver});
  290.         mapped_ver = tmp;
  291.     }
  292.     return {id, es.size()};
  293. }
  294.  
  295. vector<int> G[MAX_N];
  296. int visit[MAX_N];
  297. vector<P> ot;
  298. vector<int> ver_list;
  299.  
  300. void dfs(const int u, const int p, LCA& lca){
  301.     visit[u] = 1;
  302.     for(const int v : G[u]){
  303.         if(v == p) continue;
  304.         if(visit[v] == 0){
  305.             lca.add_edge(u, v);
  306.             dfs(v, u, lca);
  307.         }else if(visit[v] == 1){
  308.             ver_list.push_back(u), ver_list.push_back(v);
  309.             ot.push_back({u, v});
  310.         }
  311.     }
  312.     visit[u] = 2;
  313. }
  314.  
  315. int main()
  316. {
  317.     cin.tie(0);
  318.     ios::sync_with_stdio(false);
  319.     int n, m;
  320.     cin >> n >> m;
  321.     rep(i, m){
  322.         int a, b;
  323.         cin >> a >> b;
  324.         --a, --b;
  325.         G[a].pb(b), G[b].pb(a);
  326.     }
  327.     if(m == n-1){
  328.         cout << "0\n";
  329.         return 0;
  330.     }
  331.     LCA lca(n);
  332.     dfs(0, -1, lca);
  333.     lca.build();
  334.     zip(ver_list);
  335.     unordered_map<int, int> mp;
  336.     auto res = lca.construct_virtual_tree(ver_list, mp);
  337.     int N = res.first, M = res.second;
  338.     FindingAllCycles fac(N);
  339.     for(const P& e : es){
  340.         fac.add_edge(e.first, e.second), fac.add_edge(e.second, e.first);
  341.     }
  342.     for(const P& p : ot){
  343.         const int u = mp[p.first], v = mp[p.second];
  344.         fac.add_edge(u, v), fac.add_edge(v, u);
  345.         ++M;
  346.     }
  347.     cout << (fac.solve(false) - M) / 2 << "\n";
  348.     return 0;
  349. }
  350.  
Runtime error #stdin #stdout #stderr 0s 5908KB
comments (?)
stdin 
Standard input is empty
stdout 
Standard output is empty
stderr 
terminate called after throwing an instance of 'std::length_error'
  what():  vector::reserve
https://ideone.com/UFgrSx
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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