Question

我在网站（https://brilliant.org/wiki/depth-first-search-dfs/）中查看了深度优先搜索的代码。然而，实现似乎是错误的。这是他们发布的代码

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

此特定行会抛出错误

stack.extend(graph[vertex] - visited)

这是我的完整程序

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

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

print(depth_first_search(graph, 'A'))

这是程序遇到的错误

File "/home/souvik/Sublime-text programs/TestCode124.py", line 47, in 
depth_first_search
    stack.extend(graph[vertex] - visited)
TypeError: unsupported operand type(s) for -: 'list' and 'set'

代码有什么问题？

Answer 1

您将graph的值定义为列表，但该函数期望它们是集合：

graph = {
         'A': {'B', 'S'}, 
         'B': {'A'}, 
         'C': {'S', 'F', 'D', 'E'},
         ...
        }

实施深度优先搜索的代码错误

1 个答案: