二叉树235|701|450

235二叉搜索树的最近公共祖先

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if not root:
            return None
        
        if root.val > p.val and root.val > q.val:
            return self.lowestCommonAncestor(root.left, p, q)
        elif root.val < p.val and root.val < q.val:
            return self.lowestCommonAncestor(root.right, p, q)
        elif (p.val <= root.val and root.val <= q.val) or (q.val <= root.val and root.val <= p.val):
            return root

701二叉搜索树中的插入操作

# 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 insertIntoBST(self, root: Optional[TreeNode], val: int) -> Optional[TreeNode]:
        if not root:
            node = TreeNode(val)
            return node
        
        if val < root.val:
            root.left = self.insertIntoBST(root.left, val)
        if val > root.val:
            root.right = self.insertIntoBST(root.right, val)
        
        return root

450删除二叉搜索树中的节点

# 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 deleteNode(self, root: Optional[TreeNode], key: int) -> Optional[TreeNode]:
        return self.traversal(root, key)

    def traversal(self, root, key):
        if not root:
            return
        if root.val == key:
            if not root.left and not root.right:
                return None
            elif not root.left and root.right:
                return root.right
            elif root.left and not root.right:
                return root.left
            elif root.left and root.right:
                cur = root.right
                while cur.left:
                    cur = cur.left
                cur.left = root.left
                return root.right
        if root.val < key:
            root.right = self.traversal(root.right, key)
        if root.val > key:
            root.left = self.traversal(root.left, key)

        return root