# Dijkstra’s Algorithm

## No description

Files
• main.py
main.py
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```
```graph = {'a':{'b':10,'c':3},'b':{'c':1,'d':2},'c':{'b':4,'d':8,'e':2},'d':{'e':7},'e':{'d':9}}
#Dictionary of the graph 'a':{'b':10,'c':3} are the a Connection

def dijkstra(graph,start,goal):
shortest_distance = {} #Constantly updated
predecessor = {}
unseenNodes = graph #Checks every Node
infinity = 99999
path = []

#Set all nodes to infinity except for the starting node.ConnectionRefusedError
for node in unseenNodes:
shortest_distance[node] = infinity
continue
shortest_distance[start] = 0

#Loop through the unseenNodes until there are none left so we need to check if the dictionary is empty.
#Finds minimum Node.ConnectionRefusedError
while unseenNodes:
minNode = None
for node in unseenNodes:
if minNode == None:
minNode = node
elif shortest_distance[node] < shortest_distance[minNode]:
minNode = node
else:
a = 1

#Now the minimumNode has been identified, we need to check in all it’s child nodes and their weights.
#Works out length
for childNode, weight in graph[minNode].items():
if (weight + shortest_distance[minNode]) < shortest_distance[childNode]:
shortest_distance[childNode] = weight + shortest_distance[minNode]
predecessor[childNode] = minNode
else:
a = 2
unseenNodes.pop(minNode)

#Runs path backwards and records everything
currentNode = goal
while currentNode != start:
try:
path.insert(0,currentNode)
currentNode = predecessor[currentNode]
except KeyError:
print("Error")
break

if shortest_distance[goal] != infinity:
print("Shortest distance =",str(shortest_distance[goal]))
print("Path =",str(path))

#User inputs
start = str(input("Enter start: "))
goal = str(input("Enter goal: "))
graph = {'a':{'b':10,'c':3},'b':{'c':1,'d':2},'c':{'b':4,'d':8,'e':2},'d':{'e':7},'e':{'d':9}}
dijkstra(graph,start,goal)```
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