Prim idea

Start at a vertex, add the cheapest edge each step.

Prim's algorithm finds the MST by growing it from a single node. At each step, the node connected with the lowest-weight edge is added to the tree.

While Kruskal sorts edges, Prim grows the tree. Both give the same MST weight but progress differently.

Adjacency matrix

Prim works with an adjacency matrix. graph[i][j] is the edge weight between i and j; if no edge, it is 0. The matrix is symmetric.

All neighbors of a node are visible at a glance. This makes it easy to pick the lowest-weight edge.

Write init_graph(). Return the adjacency matrix. Print it with print(init_graph()).

Show example solution

def init_graph():
    # Return adjacency matrix
    return [[0, 10, 6, 5], [10, 0, 0, 15], [6, 0, 0, 4], [5, 15, 4, 0]]
print(init_graph())