[英]Recursively obtaining path to node in binary tree
I am having issues getting the path to a node in a binary tree. 我在获取二叉树中节点的路径时遇到问题。 Specifically, I don't know how to pop elements off of the stack as I return from a stack frame. 具体来说,当我从堆栈框架返回时,我不知道如何从堆栈中弹出元素。
def getPath(self, target):
stack = []
def _getPath(head):
nonlocal stack
nonlocal target
stack.append(head)
if head.value == target:
return stack
if head.left is not None:
_getPath(head.left)
if head.right is not None:
_getPath(head.right)
_getPath(self.root)
return stack
Currently, the stack will contain all of the elements in the tree. 当前,堆栈将包含树中的所有元素。
A problem here is: the information of when the target is found has to be propagated back to the called instances of getPath
. 这里的问题是:关于何时找到目标的信息必须传播回getPath
的调用实例。 The construction of the stack is kind of a "side effect" of the finding. 堆叠的构造是该发现的“副作用”。 Therefore I propose you return a boolean value in getPath
, that is True iff the target was found within the subtree currently investigated. 因此,我建议您在getPath
返回一个布尔值,如果在当前调查的子树中找到目标,则返回True。 Then we know we have to attach a value to the "stack": 然后,我们知道必须将一个值附加到“堆栈”:
def getPath(self, target):
stack = []
def _getPath(head):
nonlocal stack
nonlocal target
if head.value == target:
stack.append(head)
return True
for child in (head.left, head.right):
if child is not None:
if _getPath(child):
stack.append(head)
return True
return False
_getPath(self.root)
return reversed(stack)
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