python数据结构之图的实现方法

graph = {'A': ['B', 'C'],
       'B': ['C', 'D'],
       'C': ['D'],
       'D': ['C'],
       'E': ['F'],
       'F': ['C']}

def find_path(graph, start, end, path=[]):
    path = path + [start]
    if start == end:
      return path
    if not graph.has_key(start):
      return None
    for node in graph[start]:
      if node not in path:
        newpath = find_path(graph, node, end, path)
        if newpath: return newpath
    return None

def find_all_paths(graph, start, end, path=[]):
    path = path + [start]
    if start == end:
      return [path]
    if not graph.has_key(start):
      return []
    paths = []
    for node in graph[start]:
      if node not in path:
        newpaths = find_all_paths(graph, node, end, path)
        for newpath in newpaths:
          paths.append(newpath)
    return paths

def find_shortest_path(graph, start, end, path=[]):
    path = path + [start]
    if start == end:
      return path
    if not graph.has_key(start):
      return None
    shortest = None
    for node in graph[start]:
      if node not in path:
        newpath = find_shortest_path(graph, node, end, path)
        if newpath:
          if not shortest or len(newpath) < len(shortest):
            shortest = newpath
    return shortest