Question

我有以下遍历树对象的代码，但是找不到密钥时我无法返回节点对象。它给了我NoneType而不是。对象很简单，包含在下面。

class StructureTree:
    def __init__(self, issueID, depth):
        self.issueID = issueID
        self.depth = depth
        self.children = []
        self.worklog_data_rows = []
        self.structure_data_row = [] #contains issue data for any issue found in the global structure


    def addChild(self, elem):
        self.children += [elem]

    def __repr__(self):
        return "<%d : %d>" % (self.issueID, self.depth)


class StructureForest:
    def __init__(self):

        self.trees = []
        self.roots =[]

    def addRoot(self, root):
        self.roots += [root]

def DFS(node, key):
'''
Depth First Traversal (In-order).
@node -- int
@key -- int
'''
    if node.issueID == key:
        print "Found!"
        return node
    else:
        for child in node.children:
            print "here"
            return DFS(child, key)


def search_node(n_tree_forest, key):
'''
Traverses entire forest.
@key -- int
'''
    for root in n_tree_forest.roots:
       val = DFS(root, key)
       return val

Answer 1

您永远不会在main函数或任何递归步骤中返回值。两次拨打DFS时都需要执行return DFS(..., ...)。

Answer 2

您好我认为当您进入必须做的正确递归的else语句时，问题看起来并没有返回任何内容。修改您的DFS方法......

def DFS(node, key):

    if node.issueID == key:
        print "Found!"
        return node.issueID
    else:
        for child in node.children:
            print "here"
            val = DFS(child, key)
            if val: return val
         return False

深度优先搜索不返回正确的对象类型

2 个答案: