/
topsort.cpp
64 lines (58 loc) · 1.75 KB
/
topsort.cpp
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// works but visit same node twice in case like (1->2, 1->3, 3->2)
bool hasLoop(int node, vector<vector<int>>& adj, vector<bool>& marked) {
if(marked[node]) {
return true;
}
marked[node] = true;
for(int i = 0; i < (int)adj[node].size(); ++i) {
int neigh = adj[node][i];
if(hasLoop(neigh, adj, marked)) {
return true;
}
}
marked[node] = false;
return false;
}
// The Cormen way
enum {WHITE, GRAY, BLACK};
bool hasLoop2(int node, vector<vector<int>>& adj, vector<int>& color) {
if(color[node] == BLACK) {
return false;
}
if(color[node] == GRAY) {
return true;
}
color[node] = GRAY;
for(int i = 0; i < (int)adj[node].size(); ++i) {
int neigh = adj[node][i];
// if self loop allowed
// if(neigh == node) continue;
if(hasLoop2(neigh, adj, color)) {
return true;
}
}
color[node] = BLACK;
return false;
}
void topsortUtil(int u, vector<vector<int>>& adj, vector<bool>& visited, vector<int>& result
/*, vector<int>& parent, vector<int>& discover, vector<int>& finish, int& time */) {
visited[u] = true;
// discover[u] = ++time;
for(int i = 0; i < (int)adj[u].size(); i++) {
if(!visited[adj[u][i]]) {
// parent[adj[u][i]] = u;
topsortUtil(adj[u][i], adj, visited, result/*, parent, discover, finish, time */);
}
}
result.push_back(u);
// finish[u] = ++time;
}
void topsort(int n, vector<vector<int>>& adj, vector<int>& result) {
vector<bool> visited(n + 1, false);
for(int i = 0; i < n; i++) {
if(!visited[i]) {
topsortUtil(i, adj, visited, result);
}
}
// reverse(result.begin(), result.end());
}