#include <cstdio> #include <cstring> #include <vector> #include <algorithm> int N,M; bool cycles; std::vector<int> edges[500100]; bool visited[500100]; int parents[500100][20]; int start[500100]; int finish[500100]; int top[500100]; int expected[500100]; int cycle_begin[500100]; int cycle_end[500100]; int skip_begin[500100]; int skip_end[500100]; void searchParent(int v) { static int ts = 0; visited[v] = true; start[v] = ++ts; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { parents[n][0] = v; searchParent(n); } } finish[v] = ++ts; } void buildParents() { int level = 1; int dist = 2; while (dist <= N) { for (int i=1; i<= N; ++i) { parents[i][level] = parents[parents[i][level-1]][level-1]; } level++; dist <<= 1; } } //is a parent of b bool isParent(int a, int b) { return start[a]<=start[b] && finish[a]>=finish[b]; } int getCommonParent(int a, int b) { if (isParent(a,b)) return a; if (parents[a][0]==0) return 0; int l=0, r=19; while (l<r) { //find first parent int m = (l+r)/2; if (parents[a][m]==0 || isParent(parents[a][m], b)) r=m; else l=m+1; } if (l==0) return parents[a][0]; else return getCommonParent(parents[a][l-1], b); } int dfs(int v) { int res = 0; visited[v] = true; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { //tree edge res += dfs(n); cycle_begin[v] += cycle_begin[n]; cycle_begin[v] -= cycle_end[n]; if (!top[v] || isParent(top[n],top[v])) top[v] = top[n]; } else if (isParent(n,v)) { //back edge res++; cycles = true; cycle_begin[v] += 1; cycle_end[n] += 1; if (!top[v] || isParent(n,top[v])) top[v] = n; } else if (start[v] < start[n] && finish[v] > finish[n]) { //forward if (top[n] > 0 && start[top[n]] <= start[v]) { skip_begin[v] += 1; skip_end[n] += 1; } } else if (start[v] > start[n]) { //cross int parent = getCommonParent(v,n); if (parent && top[n] > 0 && start[top[n]] <= start[parent]) { skip_begin[parent] += 1; skip_end[n] += 1; } } } return res; } void _getResult(int v, int exp, int &skip, std::vector<int>& result) { visited[v] = true; skip -= skip_end[v]; //printf("%d %d %d\n",v,cycle_begin[v],skip); if (cycle_begin[v]==exp && skip==0) result.push_back(v); skip += skip_begin[v]; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { _getResult(n, exp, skip, result); } } } std::vector<int> getResult(int v) { std::vector<int> res; int skip = 0; _getResult(v, expected[v], skip, res); return res; } int main() { scanf("%d %d",&N,&M); for (int i=0; i<M; ++i) { int a,b; scanf("%d %d",&a,&b); edges[a].push_back(b); } memset(visited,0,sizeof(visited)); memset(parents,0,sizeof(parents)); memset(start,0,sizeof(start)); memset(finish,0,sizeof(finish)); memset(expected,0,sizeof(expected)); memset(top,0,sizeof(top)); memset(cycle_begin,0,sizeof(cycle_begin)); memset(cycle_end,0,sizeof(cycle_end)); memset(skip_begin,0,sizeof(skip_begin)); memset(skip_end,0,sizeof(skip_end)); //look for parent for (int i=1; i<=N; ++i) { if (!visited[i]) { searchParent(i); } } //build parents array buildParents(); //detect cycles int components = 0; memset(visited,0,sizeof(visited)); for (int i=1; i<=N; ++i) { if (!visited[i]) { cycles = false; expected[i] = dfs(i); if (cycles) ++components; } } //result if (components==0) printf("NIE\n"); else if (components>1) printf("0\n"); else { std::vector<int> result; memset(visited,0,sizeof(visited)); for (int i=1; i<=N && result.size()==0; ++i) { if (!visited[i] && expected[i]>0) { result = getResult(i); } } std::sort(result.begin(), result.end()); printf("%d\n",(int)result.size()); for (int i=0; i<result.size(); ++i) printf("%d ",result[i]); } 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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 | #include <cstdio> #include <cstring> #include <vector> #include <algorithm> int N,M; bool cycles; std::vector<int> edges[500100]; bool visited[500100]; int parents[500100][20]; int start[500100]; int finish[500100]; int top[500100]; int expected[500100]; int cycle_begin[500100]; int cycle_end[500100]; int skip_begin[500100]; int skip_end[500100]; void searchParent(int v) { static int ts = 0; visited[v] = true; start[v] = ++ts; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { parents[n][0] = v; searchParent(n); } } finish[v] = ++ts; } void buildParents() { int level = 1; int dist = 2; while (dist <= N) { for (int i=1; i<= N; ++i) { parents[i][level] = parents[parents[i][level-1]][level-1]; } level++; dist <<= 1; } } //is a parent of b bool isParent(int a, int b) { return start[a]<=start[b] && finish[a]>=finish[b]; } int getCommonParent(int a, int b) { if (isParent(a,b)) return a; if (parents[a][0]==0) return 0; int l=0, r=19; while (l<r) { //find first parent int m = (l+r)/2; if (parents[a][m]==0 || isParent(parents[a][m], b)) r=m; else l=m+1; } if (l==0) return parents[a][0]; else return getCommonParent(parents[a][l-1], b); } int dfs(int v) { int res = 0; visited[v] = true; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { //tree edge res += dfs(n); cycle_begin[v] += cycle_begin[n]; cycle_begin[v] -= cycle_end[n]; if (!top[v] || isParent(top[n],top[v])) top[v] = top[n]; } else if (isParent(n,v)) { //back edge res++; cycles = true; cycle_begin[v] += 1; cycle_end[n] += 1; if (!top[v] || isParent(n,top[v])) top[v] = n; } else if (start[v] < start[n] && finish[v] > finish[n]) { //forward if (top[n] > 0 && start[top[n]] <= start[v]) { skip_begin[v] += 1; skip_end[n] += 1; } } else if (start[v] > start[n]) { //cross int parent = getCommonParent(v,n); if (parent && top[n] > 0 && start[top[n]] <= start[parent]) { skip_begin[parent] += 1; skip_end[n] += 1; } } } return res; } void _getResult(int v, int exp, int &skip, std::vector<int>& result) { visited[v] = true; skip -= skip_end[v]; //printf("%d %d %d\n",v,cycle_begin[v],skip); if (cycle_begin[v]==exp && skip==0) result.push_back(v); skip += skip_begin[v]; for (int i=0; i<edges[v].size(); ++i) { int n = edges[v][i]; if (!visited[n]) { _getResult(n, exp, skip, result); } } } std::vector<int> getResult(int v) { std::vector<int> res; int skip = 0; _getResult(v, expected[v], skip, res); return res; } int main() { scanf("%d %d",&N,&M); for (int i=0; i<M; ++i) { int a,b; scanf("%d %d",&a,&b); edges[a].push_back(b); } memset(visited,0,sizeof(visited)); memset(parents,0,sizeof(parents)); memset(start,0,sizeof(start)); memset(finish,0,sizeof(finish)); memset(expected,0,sizeof(expected)); memset(top,0,sizeof(top)); memset(cycle_begin,0,sizeof(cycle_begin)); memset(cycle_end,0,sizeof(cycle_end)); memset(skip_begin,0,sizeof(skip_begin)); memset(skip_end,0,sizeof(skip_end)); //look for parent for (int i=1; i<=N; ++i) { if (!visited[i]) { searchParent(i); } } //build parents array buildParents(); //detect cycles int components = 0; memset(visited,0,sizeof(visited)); for (int i=1; i<=N; ++i) { if (!visited[i]) { cycles = false; expected[i] = dfs(i); if (cycles) ++components; } } //result if (components==0) printf("NIE\n"); else if (components>1) printf("0\n"); else { std::vector<int> result; memset(visited,0,sizeof(visited)); for (int i=1; i<=N && result.size()==0; ++i) { if (!visited[i] && expected[i]>0) { result = getResult(i); } } std::sort(result.begin(), result.end()); printf("%d\n",(int)result.size()); for (int i=0; i<result.size(); ++i) printf("%d ",result[i]); } return 0; } |