Leetcode: Count Univalue Subtrees_leetcode univalue subtree-优快云博客

本文链接：https://blog.youkuaiyun.com/ayst123/article/details/48390173

本文介绍了一种算法，用于计算二叉树中所有节点值相同的子树数量。通过递归辅助函数实现，确保所有子树节点值统一，并更新计数结果。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Question

Given a binary tree, count the number of uni-value subtrees.

A Uni-value subtree means all nodes of the subtree have the same value.

For example:
Given binary tree,
5
/ \
1 5
/ \ \
5 5 5
return 4.

Hide Tags Tree

Solution

# 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 countUnivalSubtrees(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """

        self.res = 0

        if root==None:
            return self.res

        self.helper(root)
        return self.res

    def helper(self, root):
        if root.left==None and root.right==None:
            self.res += 1
            return True
        if root.left==None and root.right!=None:
            r = self.helper(root.right)
            if r and root.val==root.right.val:
                self.res += 1
                return True
            else:
                return False
        elif root.right==None:
            l = self.helper(root.left)
            if l and root.val==root.left.val:
                self.res += 1
                return True
            else:
                return False
        else:
            l = self.helper(root.left)
            r = self.helper(root.right)
            if l and r and root.val==root.left.val and root.val==root.right.val:
                self.res += 1
                return True
            else:
                return False