# Adjacency list representation of undirected graph in python

Python program for Adjacency list representation of undirected graph. Here problem description and explanation.

```
# Python 3 Program for
# Undirected graph representation by using adjacency list
class AjlistNode :
# Vertices node key
def __init__(self, id) :
# Set value of node key
self.id = id
self.next = None
class Vertices :
def __init__(self, data) :
self.data = data
self.next = None
self.last = None
class Graph :
# Number of Vertices
def __init__(self, size) :
# Set value
self.size = size
self.node = [None] * (size)
self.setData()
# Set initial node value
def setData(self) :
if (self.size <= 0) :
print("\nEmpty Graph")
else :
index = 0
while (index < self.size) :
self.node[index] = Vertices(index)
index += 1
# Connect two nodes
def connect(self, start, last) :
edge = AjlistNode(last)
if (self.node[start].next == None) :
self.node[start].next = edge
else :
# Add edge at the end
self.node[start].last.next = edge
# Get last edge
self.node[start].last = edge
# Handling the request of adding new edge
def addEdge(self, start, last) :
if (start >= 0 and start < self.size and
last >= 0 and last < self.size) :
self.connect(start, last)
if (start == last) :
# When self loop
return
self.connect(last, start)
else :
# When invalid nodes
print("\nHere Something Wrong")
def printGraph(self) :
if (self.size > 0) :
index = 0
# Print graph ajlist Node value
while (index < self.size) :
print("\nAdjacency list of vertex ", index , end = " :")
temp = self.node[index].next
while (temp != None) :
# Display graph node
print(" ", self.node[temp.id].data, end = " ")
# Visit to next edge
temp = temp.next
index += 1
def main() :
# 5 implies the number of nodes in graph
g = Graph(5)
# Connect node with an edge
g.addEdge(0, 1)
g.addEdge(0, 2)
g.addEdge(0, 4)
g.addEdge(1, 2)
g.addEdge(1, 4)
g.addEdge(2, 3)
g.addEdge(3, 4)
# print graph element
g.printGraph()
if __name__ == "__main__": main()
```

**Output**

```
Adjacency list of vertex 0 : 1 2 4
Adjacency list of vertex 1 : 0 2 4
Adjacency list of vertex 2 : 0 1 3
Adjacency list of vertex 3 : 2 4
Adjacency list of vertex 4 : 0 1 3
```

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