python數據結構之圖的實現方法

本文實例講述了python數據結構之圖的實現方法。分享給大家供大家參考。具體如下：

下面簡要的介紹下：

比如有這么一張圖：

    A -> B
    A -> C
    B -> C
    B -> D
    C -> D
    D -> C
    E -> F
    F -> C

可以用字典和列表來構建

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

找到一條路徑：

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

找到所有路徑：

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

找到最短路徑：

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