Python刷题--Graph（find_paths/BFS/DFS/iterative/recursive）

# -*- coding:UTF-8 -*-

def dfs(graph, start):
    visited, stack = set(), [start]
    while stack:
        vertex = stack.pop()
        if vertex not in visited:
            visited.add(vertex)
            stack.extend(graph[vertex] - visited)
    return visited

# DFS
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

# BFS
def find_all_paths_bfs(graph, start, end):
    todo = [[start, [start]]]
    while 0 < len(todo):
        (node, path) = todo.pop(0)
        for next_node in graph[node]:
            if next_node in path:
                continue
            elif next_node == end:
                yield path + [next_node]
            else:
                todo.append([next_node, path + [next_node]])


def recursive_dfs(graph, start, path=[]):
    '''recursive depth first search from start'''
    path = path + [start]
    for node in graph[start]:
        if not node in path:
            path = recursive_dfs(graph, node, path)
    return path


def iterative_dfs(graph, start, path=[]):
    '''iterative depth first search from start'''
    q = [start]
    while q:
        v = q.pop(0)
        if v not in path:
            path = path + [v]
            q = graph[v] + q
    return path


def iterative_bfs(graph, start, path=[]):
    '''iterative breadth first search from start'''
    q = [start]
    while q:
        v = q.pop(0)
        if not v in path:
            path = path + [v]
            q = q + graph[v]
    return path


if __name__ == '__main__':
    graph = {'A': ['B', 'C'],
             'B': ['C', 'D'],
             'C': ['D'],
             'D': ['C'],
             'E': ['F'],
             'F': ['C']}
    print find_path(graph, 'A', 'D')
    print find_all_paths(graph, 'A', 'D')
    print find_shortest_path(graph, 'A', 'D')

    print("##" * 20)

    for path in find_all_paths_bfs(graph, 'A', 'D'):
        print path

    print("##" * 20)

    '''
       +---- A
       |   /   \
       |  B--D--C
       |   \ | /
       +---- E
    '''
    graph = {'A': ['B', 'C'], 'B': ['D', 'E'], 'C': ['D', 'E'], 'D': ['E'], 'E': ['A']}
    print 'recursive dfs ', recursive_dfs(graph, 'A')
    print 'iterative dfs ', iterative_dfs(graph, 'A')
    print 'iterative bfs ', iterative_bfs(graph, 'A')

    print("##" * 20)