代码随想录训练营第III期--021--python

# 代码随想录训练营第III期--021--python

# 腿伤长时间无法运动，感觉情绪低落，连续两天打游戏，感觉自己堕落了；

#  530.二叉搜索树的最小绝对差 
class Solution:
    def getMinimumDifference(self, root: Optional[TreeNode]) -> int:
        self.ans = 999
        self.pre = 999
        def dfs(root):
            if not root: return 
            dfs(root.left)
            self.ans = min(self.ans, abs(self.pre - root.val))
            self.pre = root.val 
            dfs(root.right)
        dfs(root)
        return self.ans 
#  501.二叉搜索树中的众数 
    def findMode(self, root: Optional[TreeNode]) -> List[int]:
        pp = collections.defaultdict(int)
        def dfs(root):
            if not root: return 
            pp[root.val] += 1
            dfs(root.left) 
            dfs(root.right)
        dfs(root)
        mm = max(pp.values())
        res = []
        for i in pp.keys():
            if pp[i] == mm:
                res.append(i)
        return res
#  236. 二叉树的最近公共祖先 
# 没理解，先保存了
    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
        if root == p or root == q:
            return root 
        if root:
            left = self.lowestCommonAncestor(root.left,p,q)
            right = self.lowestCommonAncestor(root.right,p,q)
            if left and right:
                return root 
            elif not left:
                return right 
            else:
                return left 
        return None 
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