333. Largest BST Subtree (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# 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 largestBSTSubtree(self, root: Optional[TreeNode]) -> int:
        def dfs(node):
            if not node:
                return 0, inf, -inf
            l, l_min, l_max = dfs(node.left)
            r, r_min, r_max = dfs(node.right)
            if l_max < node.val < r_min:
                return l + r + 1, min(l_min, node.val), max(r_max, node.val)
            else:
                return max(l, r), -inf, inf
        return dfs(root)[0]