undirected unweighted graph for running markov chain algorithm running markov chain algorithm and calculating the number of times each node is visited transitions a a 0 9 a b 0 075 a c 0 025 b a 0 15 b b 0 8 b c 0 05 c a 0 25 c b 0 25 c c 0 5 result gettransitions a transitions 5000 result a result b result c true undirected unweighted graph for running markov chain algorithm running markov chain algorithm and calculating the number of times each node is visited transitions a a 0 9 a b 0 075 a c 0 025 b a 0 15 b b 0 8 b c 0 05 c a 0 25 c b 0 25 c c 0 5 result get_transitions a transitions 5000 result a result b result c true
from __future__ import annotations

from collections import Counter
from random import random


class MarkovChainGraphUndirectedUnweighted:
    

    def __init__(self):
        self.connections = {}

    def add_node(self, node: str) -> None:
        self.connections[node] = {}

    def add_transition_probability(
        self, node1: str, node2: str, probability: float
    ) -> None:
        if node1 not in self.connections:
            self.add_node(node1)
        if node2 not in self.connections:
            self.add_node(node2)
        self.connections[node1][node2] = probability

    def get_nodes(self) -> list[str]:
        return list(self.connections)

    def transition(self, node: str) -> str:
        current_probability = 0
        random_value = random()

        for dest in self.connections[node]:
            current_probability += self.connections[node][dest]
            if current_probability > random_value:
                return dest
        return ""


def get_transitions(
    start: str, transitions: list[tuple[str, str, float]], steps: int
) -> dict[str, int]:
    

    graph = MarkovChainGraphUndirectedUnweighted()

    for node1, node2, probability in transitions:
        graph.add_transition_probability(node1, node2, probability)

    visited = Counter(graph.get_nodes())
    node = start

    for _ in range(steps):
        node = graph.transition(node)
        visited[node] += 1

    return visited


if __name__ == "__main__":
    import doctest

    doctest.testmod()