How to get the path from the Dijkstra algorithm in Python

Question

I took the code for the Dijkstra algorithm from this website and rewrote it for my needs (see below). Now I need to implement a feature that would store the shortest path for each node. I tried implementing it using this code from Geeks for Geeks as guideline but failed miserably. Below is the code for my graph class:

class Graph: 
    max_int = 999999
    def __init__(self, vertices, adj_matrix, start, target):
        # Get the vertices
        self.vertices = vertices

        self.start = start # an integer

        self.size = len(self.vertices)

        self.adj_matrix = adj_matrix # an adjacency matrix 

    def min_distance(self, distance, shortest_path_arr):
        min_distance = self.max_int

        for i in range(self.size):
            if distance[i] < min_distance and shortest_path_arr[i] == False:
                min_distance = distance[i]
                min_index = i
        
        return min_index
    
    def dijkstra(self):
        distance = [self.max_int] * self.size
        distance[self.start] = 0
        shortest_path_arr = [False] * self.size

        for vertex in range(self.size):
            x = self.min_distance(distance, shortest_path_arr)

            shortest_path_arr[x] = True

            for i in range(self.size):
                if self.adjMatrix[x][i] > 0 and shortest_path_arr[i] == False and distance[i] > distance[x] + self.adjMatrix[x][i]:
                    distance[i] = distance[x] + self.adjMatrix[x][i]

What should I do to get the path in the right order?

Asked By: GawronDev

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Source

Answer 1

check this code:

class Graph: 
    max_int = 999999
    def __init__(self, vertices, adj_matrix, start, target):
        # Get the vertices
        self.vertices = vertices

        self.start = start # an integer
        self.target = target # an integer

        self.size = len(self.vertices)

        self.adj_matrix = adj_matrix # an adjacency matrix 

    def min_distance(self, distance, shortest_path_arr):
        min_distance = self.max_int

        for i in range(self.size):
            if distance[i] < min_distance and shortest_path_arr[i] == False:
                min_distance = distance[i]
                min_index = i
        
        return min_index

    def dijkstra(self):
        distance = [self.max_int] * self.size
        distance[self.start] = 0
        shortest_path_arr = [False] * self.size
        parent = [-1] * self.size # initialize parent array

        for vertex in range(self.size):
            x = self.min_distance(distance, shortest_path_arr)

            shortest_path_arr[x] = True

            for i in range(self.size):
                if self.adj_matrix[x][i] > 0 and shortest_path_arr[i] == False and distance[i] > distance[x] + self.adj_matrix[x][i]:
                    distance[i] = distance[x] + self.adj_matrix[x][i]
                    parent[i] = x # update parent array

        # store shortest path for each node
        shortest_path = {}
        for node in range(self.size):
            path = []
            curr = node
            while curr != -1:
                path.insert(0, curr)
                curr = parent[curr]
            shortest_path[node] = path

        return distance[self.target], shortest_path

Answered By: Mike

How to get the path from the Dijkstra algorithm in Python

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