LeetCode: 965. Univalued Binary Tree

题目

原题地址:https://leetcode.com/problems/univalued-binary-tree/

A binary tree is univalued if every node in the tree has the same value.

Return true if and only if the given tree is univalued.

Example 1:

image

Input: [1,1,1,1,1,null,1]
Output: true

Example 2:

image2

Input: [2,2,2,5,2]
Output: false

Note:

  • The number of nodes in the given tree will be in the range [1, 100].
  • Each node's value will be an integer in the range [0, 99].

解法

遍历二叉树,如果有值跟根节点的值不一样那么就是 False 否则就是 True

这个方法的 Python 代码类似下面这样:

# 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:
        if root is None:
            return True
        stack = [root]
        value = root.val

        while stack:
            node = stack.pop(0)
            if node.val != value:
                return False
            if node.left is not None:
                stack.append(node.left)
            if node.right is not None:
                stack.append(node.right)

        return True

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