Printing Paths in Dijkstra's shortest path Python3 - python-3.x

Question

I'm having issues with the code below where it's not displaying any paths for each vertex. Vertex and Distance from the source is displaying correctly, but for the path section of the output is blank. What am I missing? I would love to get some feedbacks or suggestions or even answer to this nightmare. I just can't seem to figure out what is causing the paths from displaying anything. I'm still fairly new to Python and I could really use some help!
Output of my current code
class Graph:
def minDistance(self, dist, queue):
# Initialize min value and min_index as -1
minimum = float("Inf")
min_index = -1
# from the dist array,pick one which
# has min value and is till in queue
for i in range(len(dist)):
if dist[i] < minimum and i in queue:
minimum = dist[i]
min_index = i
return min_index
def printPath(self, parent, j):
# Base Case : If j is source
if parent[j] == -1:
print()
j,
return
self.printPath(parent, parent[j])
print()
j,
def printSolution(self, dist, parent):
src = 0
print("Vertex \t\tDistance from Source\tPath")
for i in range(1, len(dist)):
print(("\n%d --> %d \t\t%d \t\t\t\t\t" % (src, i, dist[i])), end=' ')
self.printPath(parent, i)
def dijkstra(self, graph, src):
row = len(graph)
col = len(graph[0])
dist = [float("Inf")] * row
parent = [-1] * row
dist[src] = 0
queue = []
for i in range(row):
queue.append(i)
while queue:
u = self.minDistance(dist, queue)
queue.remove(u)
for i in range(col):
if graph[u][i] and i in queue:
if dist[u] + graph[u][i] < dist[i]:
dist[i] = dist[u] + graph[u][i]
parent[i] = u
self.printSolution(dist, parent)
g = Graph()
graph = [[0, 4, 0, 0, 0, 0, 0, 8, 0],
[4, 0, 8, 0, 0, 0, 0, 11, 0],
[0, 8, 0, 7, 0, 4, 0, 0, 2],
[0, 0, 7, 0, 9, 14, 0, 0, 0],
[0, 0, 0, 9, 0, 10, 0, 0, 0],
[0, 0, 4, 14, 10, 0, 2, 0, 0],
[0, 0, 0, 0, 0, 2, 0, 1, 6],
[8, 11, 0, 0, 0, 0, 1, 0, 7],
[0, 0, 2, 0, 0, 0, 6, 7, 0]
]
g.dijkstra(graph, 0)

Answer 1

The basic issue with your code is that the printPath method is only outputting blanks and secondly, the printSolution method is not including the results of the printPath method. To fix these problems:
1 rewrite the printPath function as below:
def printPath(self, parent, j, l):
# Returns a list from destination to source
# Base case when j = source
if parent[j] == -1:
return l
else:
l.append(j)
return self.printPath(parent, parent[j], l)
Then rewrite the printSolution method as follows:
Note: I used the f format structure to simplify my print statement
def printSolution(self, dist, parent):
src = 0
print("Vertex \t\tDistance from Source\tPath")
for i in range(1, len(dist)):
st = f"\n{src} --> {i}\t\t{dist[i]}\t\t\t\t\t{self.printPath(parent,i,[])[::-1]}"
#print(("\n%d --> %d \t\t%d \t\t\t\t\t" % (src, i, dist[i])), end=' ')
#self.printPath(parent, i)
print (st)