Kumayl Fazal - 2 months ago 34

Python Question

I am trying to implement Dijkstra’s algorithm on my python code but I can't really get the algorithm right. The algorithm I am using is from this youtube link: https://www.youtube.com/watch?v=pVfj6mxhdMw

So basically my class has these 3 variables:

`self.nodes = [] #a,b,c`

self.neighbours = {} # a:[b,c], b:[c], c:[a]

self.weights = {} #[a,b] = 2, [a,c] = 5

Here is how I partially implemented my shortest path function using the algorithm provided in the video:

`def dijkstra(self, start, end):`

nodes = {}

for n in self.nodes:

if n == start:

nodes[n] = 0

else:

nodes[n] = float('inf')

unvisited = self.neighbours

visited = []

current_node = start

current_distance = 0

while unvisited:

for n in unvisited[current_node]:

print(n)

#calc_weight = nodes[n] + self.weights[n, current_node]

#if (unvisited[n] is None or calc_weight > nodes[n]):

#nodes[n] = calc_weight

visited.append(current_node)

del unvisited[current_node]

if not unvisited: break

I havent really completed because I know I missing something out somewhere. Can someone please help me with this. Thank you

Answer

```
def dijkstra(self, start, end):
nodes = self.neighbours #{'A': {'B':2}, 'B': {'C':4}, ... }
unvisited = {n: 1000 for n in self.nodes} #unvisited node & distance
unvisited[start] = 0 #set start vertex to 0
visited = {} #list of all visited nodes
parent = {} #predecessors
while unvisited:
min_node = min(unvisited, key=unvisited.get) #get smallest distance
for neighbour in nodes[min_node].items():
if neighbour not in visited:
new_distance = unvisited[min_node] + nodes[min_node][neighbour]
if new_distance < unvisited[neighbour]:
unvisited[neighbour] = new_distance
parent[neighbour] = min_node
visited[min_node] = unvisited[min_node]
unvisited.pop(min_node)
print(parent, visited)
```