PythonAlgorithms/ArticulationVert.py at master · IKMalik/PythonAlgorithms · GitHub

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# check which vertexes are cut verticies/ Articulation points

class vertex:

  def __init__(self, key):

    self.neighbours = {}
    self.key = key

  def add(self, key, edge):
    self.neighbours[key] = edge

class graph:

  def __init__(self):

    self.root = {}
    self.nbnodes = 0
    self.curr = 0

  def add(self, key1, key2, edge=0):
    if key1 not in self.root:
      self.root[key1] = vertex(key1)
      self.nbnodes += 1
    if key2 not in self.root:
      self.root[key2] = vertex(key2)
      self.nbnodes += 1

    self.root[key1].add(key2, edge)
    self.root[key2].add(key1, edge)


  def cutver(self):

    visited = set()
    discovered = {}
    low_vis = {}
    parent = {}
    result = []

    for vertex in self.root:
        if vertex not in visited:
          parent[vertex] = -1
          self._cutver(vertex, parent, visited, discovered, low_vis, result)
    print(result)


  def _cutver(self, vertex, parent, visited, discovered, low_vis, result):

    visited.add(vertex)
    discovered[vertex] = self.curr
    low_vis[vertex] = self.curr
    children = 0
    self.curr += 1

    for neighbour in self.root[vertex].neighbours:

      if neighbour not in visited:
        parent[neighbour] = vertex
        children += 1
        self._cutver(neighbour, parent, visited, discovered, low_vis, result)

        low_vis[vertex] = min(low_vis[vertex], low_vis[neighbour])

        if children > 1 and parent[vertex] == -1:
          result.append(vertex)

        if parent[vertex] != -1 and low_vis[neighbour] >= discovered[vertex]:
          result.append(vertex)

      elif neighbour != parent[vertex]:
        low_vis[vertex] = min(low_vis[neighbour], discovered[vertex])


if __name__ == '__main__':
      a = graph()
      A = 'A'
      B = 'B'
      C = 'C'
      D = 'D'
      E = 'E'
      a.add(A,B)
      a.add(A,C)
      a.add(B,D)
      a.add(D,C)
      a.add(C,E)
      a.cutver()