mirror of
https://github.com/TheAlgorithms/Python.git
synced 2024-12-05 02:40:16 +00:00
4545270ace
* Fix mypy error for frequent_pattern_graph_miner.py * Fix mypy error for markov_chain.py
85 lines
2.0 KiB
Python
85 lines
2.0 KiB
Python
from __future__ import annotations
|
|
|
|
from collections import Counter
|
|
from random import random
|
|
|
|
|
|
class MarkovChainGraphUndirectedUnweighted:
|
|
"""
|
|
Undirected Unweighted Graph for running Markov Chain Algorithm
|
|
"""
|
|
|
|
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]:
|
|
"""
|
|
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
|
|
"""
|
|
|
|
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()
|