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  1. from collections import namedtuple, defaultdict
  2.  
  3. Resistor = namedtuple('Resistor', ['node1', 'node2', 'value'])
  4.  
  5.  
  6. class Circuit(object):
  7.     def __init__(self, start, end, resistors):
  8.         self.endpoints = (start, end)
  9.         self.network = defaultdict(list)
  10.         for r in resistors:
  11.             self.network[tuple(sorted({r.node1, r.node2}))].append(int(r.value))
  12.  
  13.     def nodes(self):
  14.         nodes = set()
  15.         for n in self.network.keys():
  16.             nodes = nodes.union(set(n))
  17.         return nodes
  18.  
  19.     def neighbors(self, node):
  20.         neighbors = set()
  21.         for n in self.network.keys():
  22.             if node in n:
  23.                 neighbors = neighbors.union(set(n))
  24.         neighbors.remove(node)
  25.         return neighbors
  26.  
  27.     def equivalent_resistance(self):
  28.         def is_simplified():
  29.             if len(network) > 1:
  30.                 return False
  31.             if len(list(network.values())[0]) > 1:
  32.                 return False
  33.             return True
  34.  
  35.         network = self.network
  36.         while not is_simplified():
  37.             # Simplify parallel
  38.             for nodes, resistances in network.items():
  39.                 if len(resistances) == 1:
  40.                     continue
  41.                 equivalent = 1 / sum(1 / x for x in resistances)
  42.                 network[nodes] = [equivalent]
  43.             # Simplify serial
  44.             for node in self.nodes():
  45.                 if node in self.endpoints:
  46.                     continue
  47.                 neighbors = sorted(self.neighbors(node))
  48.                 if len(neighbors) == 2:
  49.                     key1 = tuple(sorted((neighbors[0], node)))
  50.                     key2 = tuple(sorted((neighbors[1], node)))
  51.                     r1 = network[key1]
  52.                     r2 = network[key2]
  53.                     if len(r1) != 1 or len(r2) != 1:
  54.                         continue
  55.                     r1 = r1[0]
  56.                     r2 = r2[0]
  57.                     del network[key1]
  58.                     del network[key2]
  59.                     network[tuple(neighbors)].append(r1 + r2)
  60.         return list(network.values())[0][0]
  61.  
  62.  
  63. sample = '''A B C D E F
  64. A C 5
  65. A B 10
  66. D A 5
  67. D E 10
  68. C E 10
  69. E F 15
  70. B F 20'''
  71.  
  72. nodes = sample.splitlines()[0].split()
  73. resistors = [Resistor(*line.split()) for line in sample.splitlines()[1:]]
  74. c = Circuit(nodes[0], nodes[-1], resistors)
  75. print(c.equivalent_resistance())
Success #stdin #stdout 0.03s 10192KB
comments ()
stdin 
Standard input is empty
stdout 
12.857142857142858
https://ideone.com/8wqPXI
language:
Python 3 (python  3.12)
created:
8 years ago
visibility:
public

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