//#define __DEBUG #include <iostream> #include <vector> #include <set> using namespace std; #define REP(x,n) for(int x=0;x<(n);++x) #define VAR(x,n) __typeof(n) x = (n) #define FOREACH(x,n) for(VAR(x,(n).begin());x!=(n).end();++x) int m,n; const int MAX_N = 500001; struct Node: vector<int> { int parent; int vis_nr; bool active; Node(): parent(-1), vis_nr(-1), active(false) {} } g[MAX_N]; int minCycleLength = 1000000000; int minCycleNode = -1; int disabled=-1; int cycle[MAX_N]; void printNodes(int youngest, int eldest) { int i=0; for(int x=youngest; x!=g[eldest].parent && x!=-1; x=g[x].parent) #ifdef __DEBUG { cerr << x << " "; cycle[i++] = x; } cerr << endl; #else cycle[i++] = x; #endif } bool Dfs(int start, bool forceReturn=false) { #ifdef __DEBUG cerr<<"Dfs "<<start<<"; vis_nr "<<g[start].vis_nr<<"; "<<g[start].size()<<" krawedzi"<<endl; #endif if(start==disabled) { #ifdef __DEBUG cerr<< " disabled"<<endl; #endif return false; } g[start].active = true; bool result=false; FOREACH(it, g[start]) if(g[*it].vis_nr == -1) { #ifdef __DEBUG cerr<<" "<<*it<<" do odwiedzenia"<<endl; #endif g[*it].vis_nr = g[start].vis_nr+1; g[*it].parent = start; if(Dfs(*it, forceReturn) && forceReturn) { result=true; break; } } else if (g[*it].active) { int cycleLength = g[start].vis_nr - g[*it].vis_nr + 1; #ifdef __DEBUG cerr<<" "<<*it<<" w cyklu"<<endl; cerr << "Cykl " << cycleLength << endl; #endif result=true; if(forceReturn) break; if(cycleLength < minCycleLength) { minCycleLength = cycleLength; minCycleNode = start; printNodes(start, *it); } } #ifdef __DEBUG else cerr<<" "<<*it<<" - nic szczegolnego"<<endl; #endif g[start].active = false; return result; } bool Dfs(bool forceReturn=false) { #ifdef __DEBUG cerr<<"##DFS## "<<forceReturn<<endl; #endif REP(x,n) g[x].vis_nr = -1; REP(x,n) if(g[x].vis_nr == -1) { g[x].vis_nr = 0; if(Dfs(x, forceReturn) && forceReturn) { #ifdef __DEBUG cerr << "##DFS returns true"<<endl; #endif return true; } } #ifdef __DEBUG cerr<<" ##DFS returns false"<<endl; #endif return false; } bool hasCycle(int dis) { #ifdef __DEBUG cerr<<"$$HasCycle$$ "<<dis<<endl; #endif disabled = dis; return Dfs(true); } int main() { ios_base::sync_with_stdio(0); cin>>n>>m; int a,b; REP(x,m) { cin>>a>>b; g[a-1].push_back(b-1); } Dfs(); if(minCycleNode == -1) { cout<<"NIE"; } else { set<int> result; REP(x, minCycleLength) if(!hasCycle(cycle[x])) result.insert(cycle[x]+1); cout<<result.size()<<endl; FOREACH(it, result) cout<<*it<<" "; } 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 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 | //#define __DEBUG #include <iostream> #include <vector> #include <set> using namespace std; #define REP(x,n) for(int x=0;x<(n);++x) #define VAR(x,n) __typeof(n) x = (n) #define FOREACH(x,n) for(VAR(x,(n).begin());x!=(n).end();++x) int m,n; const int MAX_N = 500001; struct Node: vector<int> { int parent; int vis_nr; bool active; Node(): parent(-1), vis_nr(-1), active(false) {} } g[MAX_N]; int minCycleLength = 1000000000; int minCycleNode = -1; int disabled=-1; int cycle[MAX_N]; void printNodes(int youngest, int eldest) { int i=0; for(int x=youngest; x!=g[eldest].parent && x!=-1; x=g[x].parent) #ifdef __DEBUG { cerr << x << " "; cycle[i++] = x; } cerr << endl; #else cycle[i++] = x; #endif } bool Dfs(int start, bool forceReturn=false) { #ifdef __DEBUG cerr<<"Dfs "<<start<<"; vis_nr "<<g[start].vis_nr<<"; "<<g[start].size()<<" krawedzi"<<endl; #endif if(start==disabled) { #ifdef __DEBUG cerr<< " disabled"<<endl; #endif return false; } g[start].active = true; bool result=false; FOREACH(it, g[start]) if(g[*it].vis_nr == -1) { #ifdef __DEBUG cerr<<" "<<*it<<" do odwiedzenia"<<endl; #endif g[*it].vis_nr = g[start].vis_nr+1; g[*it].parent = start; if(Dfs(*it, forceReturn) && forceReturn) { result=true; break; } } else if (g[*it].active) { int cycleLength = g[start].vis_nr - g[*it].vis_nr + 1; #ifdef __DEBUG cerr<<" "<<*it<<" w cyklu"<<endl; cerr << "Cykl " << cycleLength << endl; #endif result=true; if(forceReturn) break; if(cycleLength < minCycleLength) { minCycleLength = cycleLength; minCycleNode = start; printNodes(start, *it); } } #ifdef __DEBUG else cerr<<" "<<*it<<" - nic szczegolnego"<<endl; #endif g[start].active = false; return result; } bool Dfs(bool forceReturn=false) { #ifdef __DEBUG cerr<<"##DFS## "<<forceReturn<<endl; #endif REP(x,n) g[x].vis_nr = -1; REP(x,n) if(g[x].vis_nr == -1) { g[x].vis_nr = 0; if(Dfs(x, forceReturn) && forceReturn) { #ifdef __DEBUG cerr << "##DFS returns true"<<endl; #endif return true; } } #ifdef __DEBUG cerr<<" ##DFS returns false"<<endl; #endif return false; } bool hasCycle(int dis) { #ifdef __DEBUG cerr<<"$$HasCycle$$ "<<dis<<endl; #endif disabled = dis; return Dfs(true); } int main() { ios_base::sync_with_stdio(0); cin>>n>>m; int a,b; REP(x,m) { cin>>a>>b; g[a-1].push_back(b-1); } Dfs(); if(minCycleNode == -1) { cout<<"NIE"; } else { set<int> result; REP(x, minCycleLength) if(!hasCycle(cycle[x])) result.insert(cycle[x]+1); cout<<result.size()<<endl; FOREACH(it, result) cout<<*it<<" "; } return 0; } |