diff --git a/problems/0669.修剪二叉搜索树.md b/problems/0669.修剪二叉搜索树.md index 18d8a0cc..95372d61 100644 --- a/problems/0669.修剪二叉搜索树.md +++ b/problems/0669.修剪二叉搜索树.md @@ -271,64 +271,72 @@ class Solution { ## Python -**递归** - +递归法(版本一) ```python -# Definition for a binary tree node. -# class TreeNode: -# def __init__(self, val=0, left=None, right=None): -# self.val = val -# self.left = left -# self.right = right class Solution: def trimBST(self, root: TreeNode, low: int, high: int) -> TreeNode: - ''' - 确认递归函数参数以及返回值:返回更新后剪枝后的当前root节点 - ''' - # Base Case - if not root: return None - - # 单层递归逻辑 + if root is None: + return None if root.val < low: - # 若当前root节点小于左界:只考虑其右子树,用于替代更新后的其本身,抛弃其左子树整体 + # 寻找符合区间 [low, high] 的节点 return self.trimBST(root.right, low, high) - - if high < root.val: - # 若当前root节点大于右界:只考虑其左子树,用于替代更新后的其本身,抛弃其右子树整体 + if root.val > high: + # 寻找符合区间 [low, high] 的节点 return self.trimBST(root.left, low, high) + root.left = self.trimBST(root.left, low, high) # root.left 接入符合条件的左孩子 + root.right = self.trimBST(root.right, low, high) # root.right 接入符合条件的右孩子 + return root - if low <= root.val <= high: - root.left = self.trimBST(root.left, low, high) - root.right = self.trimBST(root.right, low, high) - # 返回更新后的剪枝过的当前节点root - return root ``` - -**迭代** - +递归法(版本二)精简 ```python class Solution: - def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]: - if not root: return root - # 处理头结点,让root移动到[L, R] 范围内,注意是左闭右开 - while root and (root.val < low or root.val > high): - if root.val < low: # 小于L往右走 - root = root.right - else: # 大于R往左走 - root = root.left - # 此时root已经在[L, R] 范围内,处理左孩子元素小于L的情况 + def trimBST(self, root: TreeNode, low: int, high: int) -> TreeNode: + if root is None: + return None + if root.val < low: + return self.trimBST(root.right, low, high) + if root.val > high: + return self.trimBST(root.left, low, high) + root.left = self.trimBST(root.left, low, high) + root.right = self.trimBST(root.right, low, high) + return root + + +``` + +迭代法 +```python +class Solution: + def trimBST(self, root: TreeNode, L: int, R: int) -> TreeNode: + if not root: + return None + + # 处理头结点,让root移动到[L, R] 范围内,注意是左闭右闭 + while root and (root.val < L or root.val > R): + if root.val < L: + root = root.right # 小于L往右走 + else: + root = root.left # 大于R往左走 + cur = root + + # 此时root已经在[L, R] 范围内,处理左孩子元素小于L的情况 while cur: - while cur.left and cur.left.val < low: + while cur.left and cur.left.val < L: cur.left = cur.left.right cur = cur.left - # 此时root已经在[L, R] 范围内,处理右孩子大于R的情况 + cur = root + + # 此时root已经在[L, R] 范围内,处理右孩子大于R的情况 while cur: - while cur.right and cur.right.val > high: + while cur.right and cur.right.val > R: cur.right = cur.right.left cur = cur.right + return root + ``` ## Go