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class Graph:
    def __init__(self):
        self.graph = {}  # Dictionary to store nodes and their adjacent nodes

    def add_edge(self, node1, node2):
        # Add a bidirectional edge between node1 and node2
        if node1 not in self.graph:
            self.graph[node1] = []
        if node2 not in self.graph:
            self.graph[node2] = []

        self.graph[node1].append(node2)
        self.graph[node2].append(node1)

    def display(self):
        # Print the contents of the graph
        for node in self.graph:
            print(f"{node} -> {self.graph[node]}")

# Create a graph object
g = Graph()

# Add edges
g.add_edge('A', 'B')
g.add_edge('A', 'C')
g.add_edge('B', 'C')
g.add_edge('B', 'D')

# Display the graph
g.display()

# Graph Implementation Techniques

## 1. Defining the Graph Class

- A graph is a data structure that models a network using nodes and edges.

- The `Graph` class includes a dictionary to store nodes and their adjacent nodes.

 

```python title="Example Definition of Graph Class"
class Graph:
 def __init__(self):
 self.graph = {} # Dictionary to store nodes and their adjacent nodes
```

 

## 2. Method to Add Edges

- The `add_edge` method adds a bidirectional edge between two nodes.

- If a node is not present in the graph, the node is added with an empty list assigned.

 

```python title="Example Method to Add Edges"
def add_edge(self, node1, node2):
 if node1 not in self.graph:
 self.graph[node1] = []
 if node2 not in self.graph:
 self.graph[node2] = []

 self.graph[node1].append(node2)
 self.graph[node2].append(node1)
```

 

## 3. Graph Display Method

- The `display` method outputs the contents of the graph.

- By printing each node and its adjacent nodes, the method illustrates the structure of the graph.

 

```python title="Example Graph Display Method"
def display(self):
 for node in self.graph:
 print(f"{node} -> {self.graph[node]}")
```

 

## 4. Creating and Using a Graph Object

- Create an instance of the `Graph` class, and build the graph by adding edges.

- Call the `display` method to verify the structure of the graph.

 

```python title="Example of Creating and Using a Graph Object"
# Creating a graph object
g = Graph()

# Adding edges
g.add_edge('A', 'B')
g.add_edge('A', 'C')
g.add_edge('B', 'C')
g.add_edge('B', 'D')

# Displaying the graph
g.display()
```