#include <bits/stdc++.h> using namespace std; const int N = 500005; int n, m, a, b, size[2], intervalBegin, intervalEnd; int vis[N], S[2][N], where[N]; vector<int>V[2][N]; int visited; int specjal; void DFS(int w, int d) { vis[w] = 1; visited++; for (int i = 0; i < V[d][w].size(); i++) { int u = V[d][w][i]; if (vis[u] == 0) { DFS(u, d); } else if (vis[u] == 2 && d == 1) { swap(V[d][w][i], V[d][w].back()); V[d][w].pop_back(); i--; } } S[d][++size[d]] = w; } bool isCycle() { for (int i = 1; i <= n; i++) { vis[i] = 0; } size[0] = size[1] = 0; vis[specjal] = 1; for (int i = 1; i <= n; i++) { if (vis[i] == 0) { DFS(i, 0); } } for (int i = 1; i <= n; i++) { vis[i] = 0; } vis[specjal] = 1; visited = 0; bool ret = false; for (int i = size[0]; i >= 1; i--) { int lastVisited = visited; if (vis[S[0][i]] == 0) { int lSize = size[1]; DFS(S[0][i], 1); for (int j = lSize + 1; j <= size[1]; j++) { vis[S[1][j]] = 2; } if (visited > lastVisited + 1) { ret = true; } } } return ret; } vector<int> results; int best[N]; void findNodes() { reverse(S[1] + 1, S[1] + 1 + size[1]); for (int i = 1; i <= size[1]; i++) { where[S[1][i]] = i; } intervalEnd = 1e9; for (int i = 1; i <= size[1]; i++) { int w = S[1][i]; for (int j = 0; j < V[1][w].size(); j++) { int u = V[1][w][j]; if (where[u] != 0 && where[u] < where[w]) { intervalBegin = max(intervalBegin, where[u]); intervalEnd = min(intervalEnd, where[w]); } } } if (intervalEnd < intervalBegin) { return; } int maxi = 1e9; for (int i = size[1]; i >= 1; i--) { int w = S[1][i]; if ((maxi >= i) && (intervalBegin <= i && i <= intervalEnd)) { results.push_back(w); } best[w] = 1e9; for (int j = 0; j < V[1][w].size(); j++) { int u = V[1][w][j]; if (where[u] != 0 && i < where[u]) { best[w] = min(best[w], best[u]); } else if (where[u] != 0 && where[u] < i) { best[w] = min(best[w], where[u]); } } for (int j = 0; j < V[0][w].size(); j++) { int u = V[0][w][j]; if (where[u] != 0 && where[u] < i && where[u] >= best[w]) { maxi = min(maxi, where[u]); } } } } int main() { scanf("%d %d", &n, &m); for (int i = 1; i <= m; i++) { scanf("%d %d", &a, &b); V[0][b].push_back(a); V[1][a].push_back(b); } if (!isCycle()) { printf("NIE\n"); return 0; } findNodes(); printf("%d\n", results.size()); sort(results.begin(), results.end()); for(int i = 0; i < results.size(); i++) { printf("%d ", results[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 | #include <bits/stdc++.h> using namespace std; const int N = 500005; int n, m, a, b, size[2], intervalBegin, intervalEnd; int vis[N], S[2][N], where[N]; vector<int>V[2][N]; int visited; int specjal; void DFS(int w, int d) { vis[w] = 1; visited++; for (int i = 0; i < V[d][w].size(); i++) { int u = V[d][w][i]; if (vis[u] == 0) { DFS(u, d); } else if (vis[u] == 2 && d == 1) { swap(V[d][w][i], V[d][w].back()); V[d][w].pop_back(); i--; } } S[d][++size[d]] = w; } bool isCycle() { for (int i = 1; i <= n; i++) { vis[i] = 0; } size[0] = size[1] = 0; vis[specjal] = 1; for (int i = 1; i <= n; i++) { if (vis[i] == 0) { DFS(i, 0); } } for (int i = 1; i <= n; i++) { vis[i] = 0; } vis[specjal] = 1; visited = 0; bool ret = false; for (int i = size[0]; i >= 1; i--) { int lastVisited = visited; if (vis[S[0][i]] == 0) { int lSize = size[1]; DFS(S[0][i], 1); for (int j = lSize + 1; j <= size[1]; j++) { vis[S[1][j]] = 2; } if (visited > lastVisited + 1) { ret = true; } } } return ret; } vector<int> results; int best[N]; void findNodes() { reverse(S[1] + 1, S[1] + 1 + size[1]); for (int i = 1; i <= size[1]; i++) { where[S[1][i]] = i; } intervalEnd = 1e9; for (int i = 1; i <= size[1]; i++) { int w = S[1][i]; for (int j = 0; j < V[1][w].size(); j++) { int u = V[1][w][j]; if (where[u] != 0 && where[u] < where[w]) { intervalBegin = max(intervalBegin, where[u]); intervalEnd = min(intervalEnd, where[w]); } } } if (intervalEnd < intervalBegin) { return; } int maxi = 1e9; for (int i = size[1]; i >= 1; i--) { int w = S[1][i]; if ((maxi >= i) && (intervalBegin <= i && i <= intervalEnd)) { results.push_back(w); } best[w] = 1e9; for (int j = 0; j < V[1][w].size(); j++) { int u = V[1][w][j]; if (where[u] != 0 && i < where[u]) { best[w] = min(best[w], best[u]); } else if (where[u] != 0 && where[u] < i) { best[w] = min(best[w], where[u]); } } for (int j = 0; j < V[0][w].size(); j++) { int u = V[0][w][j]; if (where[u] != 0 && where[u] < i && where[u] >= best[w]) { maxi = min(maxi, where[u]); } } } } int main() { scanf("%d %d", &n, &m); for (int i = 1; i <= m; i++) { scanf("%d %d", &a, &b); V[0][b].push_back(a); V[1][a].push_back(b); } if (!isCycle()) { printf("NIE\n"); return 0; } findNodes(); printf("%d\n", results.size()); sort(results.begin(), results.end()); for(int i = 0; i < results.size(); i++) { printf("%d ", results[i]); } return 0; } |