Terminology:

1. If you are at a Node then the nodes connected to that node are called Neigbours

Types and Methods of Input

Non Weighted Graphs

In Non Weighted Graphs the edge value is 1.

There are two types of graphs:

1. Undirected
   In undirected graph the relation is two ways i.e. u --> v and v --> u

2. Directed
   In directed graph the relation is one way i.e. u --> v only

There are two methods of input:

1. Adjacency Matrix

int arr[n+1][n+1]; // n is number of nodes
for (i to m) { //  m is number of edges
	int r, c;
	cin >> r >> c;
	arr[r][c] = 1;
	arr[c][r] = 1; //! Remove this line for Directed Graph
}

2. Adjacency List

vector<int> arr[n+1]; // n is number of nodes
for (i to m) { //  m is number of edges
	int r, c;
	cin >> r >> c;
	arr[r].push_back(c);
	arr[c].push_back(r); //! Remove this line for Directed Graph
}

Weighted Graphs

The edges also have weights

1. For Adjacency Matrix:

int arr[n+1][n+1]; // n is number of nodes
for (i to m) { //  m is number of edges
	int r, c, wt;
	cin >> r >> c >> wt;
	arr[r][c] = wt;
	arr[c][r] = wt; //! Remove this line for Directed Graph
}

2. For Adjacency List:

vector<pair<int,int>> arr[n+1]; // Notice we have used pair here i.e. we will store both the node and the weight
for (i to m) { //  m is number of edges
	int r, c, wt;
	cin >> r >> c >> wt;
	arr[r].push_back({c, wt);
	arr[c].push_back({r. wt}); //! Remove this line for Directed Graph
}