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cycle.cpp
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cycle.cpp
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#include <iostream>
#include <list>
#include <vector>
#include <algorithm>
using namespace std;
class Graph{
private:
int numofvertices;
list<int> *ptr;
vector<int> color;
vector<int> root;
int startofcircle, endofcircle;
bool DFS(int v) {
color[v]=1;
for(int u: ptr[v]){
if(color[u]==0) {
root[u]=v;
if(DFS(u))
return true;
}
else if(color[u]==1) {
endofcircle=v;
startofcircle=u;
return true;
}
}
color[v]=2;
return false;
}
public:
Graph(int V): numofvertices(V) { ptr=new list<int>[numofvertices]; }
~Graph() { delete [] ptr;}
void addEdge (int u, int v) {
ptr[u].push_back(v);
}
bool cycle(vector<int> &cycle) {
color.assign(numofvertices, 0);
root.assign(numofvertices, -1);
startofcircle=-1;
for(int v=0; v<numofvertices; v++) {
if(color[v]==0 && DFS(v))
break;
}
if(startofcircle==-1)
return false;
else {
cycle.push_back(startofcircle);
for( int v=endofcircle; v!=startofcircle; v=root[v])
cycle.push_back(v);
reverse(cycle.begin(), cycle.end());
return true;
}
}
};