freeCodeCamp/curriculum/challenges/english/blocks/learn-algorithm-design-by-building-a-shortest-path-algorithm/655791e6cf5e03be3de73451.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
655791e6cf5e03be3de73451	Step 50	20	step-50

--description--

If you try to uncomment your function call, it won't work. You have a couple of bugs to fix. The first one happens because in the nested if you are trying to access an element that might not exist in your paths[node] list. So, you need to be sure that paths[node] is not empty before accessing paths[node][-1].

Add an additional condition to your nested if statement to ensure that paths[node] is non-empty before accessing paths[node][-1].

--hints--

You should add paths[node] as the first condition to your nested if statement. Use the and operator to combine your conditions.

({ test: () =>  {
    const shortest = __helpers.python.getDef(code, "shortest_path");
    const {function_body} = shortest;    
    assert(function_body.match(/if\s+paths\s*\[\s*node\s*\]\s+and\s+paths\s*\[\s*node\s*\]\s*\[\s*-\s*1\s*\]\s*==\s*node\s*:/));
  }
})

--seed--

--seed-contents--

my_graph = {
    'A': [('B', 3), ('D', 1)],
    'B': [('A', 3), ('C', 4)],
    'C': [('B', 4), ('D', 7)],
    'D': [('A', 1), ('C', 7)]
}

def shortest_path(graph, start):
    unvisited = list(graph)
    distances = {node: 0 if node == start else float('inf') for node in graph}
    paths = {node: [] for node in graph}
    paths[start].append(start)
    
    while unvisited:
        current = min(unvisited, key=distances.get)
        for node, distance in graph[current]:
            if distance + distances[current] < distances[node]:
                distances[node] = distance + distances[current]
--fcc-editable-region--                
                if paths[node][-1] == node:
                    paths[node] = paths[current]
--fcc-editable-region--                   
                else:
                    paths[node].extend(paths[current])
                paths[node].append(node)
        unvisited.remove(current)
    
    print(f'Unvisited: {unvisited}\nDistances: {distances}\nPaths: {paths}')
    
#shortest_path(my_graph, 'A')