530 二叉搜索树的最小绝对差

class Solution:
    def getMinimumDifference(self, root: Optional[TreeNode]) -> int:
        self.last=float('inf')
        self.temp=float('inf')
        def sub(root):
            if not root:
                return 
            sub(root.left)
            if abs(root.val-self.last)<self.temp:
                self.temp=abs(root.val-self.last)
            self.last=root.val
            sub(root.right)
            


        sub(root)
        return self.temp

501 二叉搜索树中的众数

class Solution:
    def findMode(self, root: Optional[TreeNode]) -> List[int]:
        self.rets=[]
        self.times=0
        self.lasttime=0
        self.last=None
        def sub(root):
            if not root:
                return 
            sub(root.left)
            if root.val==self.last:
                self.lasttime+=1
                
            else:
                self.last=root.val
                self.lasttime=1
            if self.times<self.lasttime:
                self.rets=[self.last]
                self.times=self.lasttime
            elif self.times==self.lasttime:
                self.rets.append(self.last)
            sub(root.right)
        sub(root)
        return self.rets

236 二叉树的最近公共祖先

class Solution:
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        self.ret=None
        def sub(root,left,right):
            if not root:
                return False
            l=sub(root.left,left,right)
            r=sub(root.right,left,right)
            if (l and r)or((root.val==p.val or root.val==q.val) and (l or r)):
                self.ret=root
            if l or r or root.val==p.val or root.val==q.val:
                return True
            return False
        sub(root,p,q)
        return self.ret