[Solved] 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.

Question

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

Python Solution

# 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: TreeNode) -> bool:
        stack = [root]
        prev = root.val
        while len(stack)!=0:
            x = stack.pop()
            if x==None:
                continue
            curr = x.val
            if prev!=curr:
                return False
            stack.append(x.left)
            stack.append(x.right)
            prev = curr
            
        return True