965.univalued-binary-tree.py

#
# @lc app=leetcode id=965 lang=python3
#
# [965] Univalued Binary Tree
#
# https://leetcode.com/problems/univalued-binary-tree/description/
#
# algorithms
# Easy (69.52%)
# Likes:    1620
# Dislikes: 60
# Total Accepted:    187.8K
# Total Submissions: 269.8K
# Testcase Example:  '[1,1,1,1,1,null,1]'
#
# A binary tree is uni-valued if every node in the tree has the same value.
# 
# Given the root of a binary tree, return true if the given tree is uni-valued,
# or false otherwise.
# 
# 
# Example 1:
# 
# 
# Input: root = [1,1,1,1,1,null,1]
# Output: true
# 
# 
# Example 2:
# 
# 
# Input: root = [2,2,2,5,2]
# Output: false
# 
# 
# 
# Constraints:
# 
# 
# The number of nodes in the tree is in the range [1, 100].
# 0 <= Node.val < 100
# 
# 
#

# @lc code=start
# 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 isUnivalTree(self, root: Optional[TreeNode]) -> bool:
        if not root:
            return True
        stk = [root]
        val = root.val
        res = []
        while stk:
            node = stk.pop()
            cur_val = node.val
            if cur_val != val:
                return False
            if node.right:
                stk.append(node.right)
            if node.left:
                stk.append(node.left)
        return True
        
# @lc code=end