Dijkstra's Shortest Path (Naive)

Dijkstra’s shortest path algorithm calculates the shortest distance between vertices in a weighted graph with non-negative edge weights. This is without a doubt one of the greatest hits of algorithms with countless applications. Those wishing to excel in computer science should take extra car to ensure they fully understand this.

The algorithm as shown in the this section is a naive implementation. Each iteration of the main while loop requires a scan over all edges to find the one with the minimum distance. While this runtime isn’t horrible, it’s possible to do much better using the implementation in the next section.

Asymptotic Complexity

$O(mn)$

Pseudo Code

dijkstra:
    G = input graph with distance of each vertex set to infinity
    v = starting vertex
    side effects: marks all vertices with the shortest distance from the starting
    vertex

    S = empty array

    v.distance = 0
    S.add(v)

    while true:
        u = find_min(G, S)
        if u is NULL or u.distance == infinity:
            break

        S.add(u)

find_min:
    G = input graph
    S = array containing all conquered vertices

    v = NULL

    for each vertex in S:
        for each edge in vertex:
            if edge.head is contained in S:
                continue

            distance = edge.tail.distance + edge.weight
            if distance < edge.head.distance
                edge.head.distance = distance

            if edge.head.distance < v.distance
                v = edge.head

    return v

Source Code

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