LeetCode-98-Validate Binary Search Tree dfs二叉树

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

class Solution(object):
    def isValidBST(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root==None:return True
        return self.dfs(root,-99999999999,0x7fffffff)
    def dfs(self,root,l,r):
        v=root.val
        if v<l or v>r:return False
        if root.left==None and root.right==None:
            return v<=r and v>=l
        flag=0
        if root.left!=None:
            flag-=1
            if self.dfs(root.left,l,v-1):flag+=1
        if root.right!=None:
            flag-=1
            if self.dfs(root.right,v+1,r):flag+=1
        return flag==0