2021-01-28

231.2的幂

if(n<=0)：return false
else if((n&n-1)==0):return true
else return false

235.二叉搜索树的最近公共祖先

class Solution(object):
    def lowestCommonAncestor(self, root, p, q):
        """
        :type root: TreeNode
        :type p: TreeNode
        :type q: TreeNode
        :rtype: TreeNode
        """
        if p.val<root.val and q.val<root.val:
            return self.lowestCommonAncestor(root.left,p,q)
        
        if p.val>root.val and q.val>root.val:
            
            return self.lowestCommonAncestor(root.right,p,q)
        
        return root

236.二叉树的最近公共祖先

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if root in (None ,p,q):
            return root 
        L = self.lowestCommonAncestor(root.left,p,q)
        R =self.lowestCommonAncestor(root.right,p,q)
        return R if None==L else L if None==R else root