RecursionError：超過最大遞歸深度 - 二叉樹

Question

在為二叉樹實現add_node和search方法時，我得到一個 RecursionError: maximum recursion depth exceeded

代碼：

class TreeNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None


class BinaryTree:
    def __init__(self, root=None):
        self.root = root

    def add_node(self, node, value):
        node = self.root
        if node is not None:
            if not node.value:
                node.value = value
            elif not node.left:
                node.left = value
            elif not node.right:
                node.right = value
            else:
                node.left = self.add_node(node.left, value)
        else:
            self.root = TreeNode(value)

    def search(self, value):
        node = self.root
        found = False
        while node is not None:
            if node.value == value:
                found = True
            if node.left:
                found = node.left.search(value)
            if node.right:
                found = found or node.left.search(value)
        return found



def main():
    binary_tree = BinaryTree()
    binary_tree.add_node(binary_tree.root, 200)
    binary_tree.add_node(binary_tree.root, 300)
    binary_tree.add_node(binary_tree.root, 100)
    binary_tree.add_node(binary_tree.root, 30)
    binary_tree.traverse_inorder(binary_tree.root)
    print(binary_tree.search(200))


if __name__ == '__main__':
    main()

錯誤：

Traceback (most recent call last):
  File ".\binary_tree_test20.py", line 51, in <module>
    main()
  File ".\binary_tree_test20.py", line 45, in main
    binary_tree.add_node(binary_tree.root, 30)
  File ".\binary_tree_test20.py", line 22, in add_node
    node.left = self.add_node(node.left, value)
  File ".\binary_tree_test20.py", line 22, in add_node
    node.left = self.add_node(node.left, value)
  File ".\binary_tree_test20.py", line 22, in add_node
    node.left = self.add_node(node.left, value)
  [Previous line repeated 995 more times]
RecursionError: maximum recursion depth exceeded

Answer 1

這是我可以給你的補救措施。

class TreeNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

def _add_node(node, value):
    if not node.value:
        node.value = value
    elif not node.left:
        node.left = TreeNode(value)
    elif not node.right:
        node.right = TreeNode(value)
    else:
        _add_node(node.left, value)

class BinaryTree:
    # ...

    def add_node(self, value):
        node = self.root
        if node is not None:
            _add_node(node, value)
        else:
            self.root = TreeNode(value)

    # ...



def main():
    binary_tree = BinaryTree()
    binary_tree.add_node(200)
    binary_tree.add_node(300)
    binary_tree.add_node(100)
    binary_tree.add_node(30)

雖然我建議只擴展TreeNode定義而不定義BinaryTree 。

Answer 2

您將獲得無限遞歸，因為您沒有使用node參數，而是將其替換為self.root 。 所以當你遞歸的時候，你每次都從根開始，永遠不會結束。

此外，行node.left = self.add_node(node.left, value)期望add_node返回新節點，但您的方法不返回任何內容。 當它更新現有節點時，它應該只返回修改后的節點； 如果它正在創建一個新節點，則返回該節點。

    def add_node(self, node, value):
        if node is not None:
            if not node.value:
                node.value = value
            elif not node.left:
                node.left = value
            elif not node.right:
                node.right = value
            else:
                node.left = self.add_node(node.left, value)
            return node
        else:
            return TreeNode(value)

你會像這樣調用這個方法：

binary_tree.root = binary_tree.add_node(binary_tree.root, 30)