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Graph.cpp
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Graph.cpp
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# include <bits/stdc++.h>
using namespace std;
class Graph{
private:
int V;
vector<int> *adj;
void explore(int s, bool *visited, int *CC, int CCnumber){
// Explores and labels all the vertices present in a connected component
visited[s] = true;
CC[s] = CCnumber;
for(auto it=adj[s].begin(); it!=adj[s].end(); it++){
if(!visited[*it])
explore(*it, visited, CC, CCnumber);
}
}
public:
Graph(int v){
this->V = v;
this->adj = new vector<int>[v];
}
void addEdge(int s, int d){
adj[s].push_back(d);
adj[d].push_back(s);
}
void explore(int s, bool *visited){
// Explores all the edges reachable from a sourse S in DFS order.
// The boolean array visited is required to be passed by the calling function.
visited[s] = true;
cout << s << " ";
for(auto it=adj[s].begin(); it!=adj[s].end(); it++){
if(!visited[*it])
explore(*it, visited);
}
}
void explore(int s, bool *visited, int *preVisit, int *postVisit, int &clock){
// Explores all the edges reachable from a sourse S in DFS order and labes their previsit and postvisit orderings.
// The int arrays preVisit and postVisit are passed by reference to store the ordering.
// clock is also passed by reference;
visited[s] = true;
preVisit[s] = clock++;
for(auto it=adj[s].begin(); it!=adj[s].end(); it++){
if(!visited[*it])
explore(*it, visited, preVisit, postVisit, clock);
}
postVisit[s] = clock++;
}
void DFS(){
// Standard DEPTH FIRST SEARCH of the
bool *visited = new bool[this->V];
for(int i=0; i<this->V; i++)
visited[i] = 0;
for(int i=0; i<this->V; i++){
if(!visited[i])
explore(i, visited);
}
}
int* connectedComponents(){
// Returns an array of size this->V containg all the different connected components labelled.
// The index i and j having same label means that they are part of the same connected component and are reachable from each other...
bool *visited = new bool[this->V];
for(int i=0; i<this->V; i++)
visited[i] = 0;
int *CC = new int[this->V];
int CCnumber = 1;
for(int i=0; i<this->V; i++){
if(!visited[i]){
explore(i, visited, CC, CCnumber);
CCnumber++;
}
}
return CC;
}
void DFS(int *preVisit, int *postVisit){
// This function takes pointers to two arrays called preVisit and postVisit and sotores the DFS ordering of vertices in the arrays
bool *visited = new bool[this->V];
for(int i=0; i<this->V; i++)
visited[i] = 0;
int clock = 0;
for(int i=0; i<this->V; i++){
if(!visited[i])
explore(i, visited, preVisit, postVisit, clock);
}
}
};
int main(){
Graph *g = new Graph(10);
g->addEdge(0, 1);
g->addEdge(0, 4);
g->addEdge(1, 2);
g->addEdge(1, 3);
g->addEdge(1, 4);
g->addEdge(2, 3);
g->addEdge(3, 4);
g->addEdge(5, 6);
g->addEdge(5, 7);
g->addEdge(8, 9);
int *prev = new int[10];
int *post = new int[10];
g->DFS(prev, post);
for(int i=0; i<10; i++)
cout << i << " : " << prev[i] << " / " << post[i] << endl;
return 0;
}