题目要求
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.
题目分析及思路
题目要求当输入的二叉树的每个结点都有相同的值则返回true，否则返回false。可以使用队列保存每个节点，用val保存root节点的值。如果弹出的数字不等于val不等于root节点就立刻返回false。如果全部判断完成之后仍然没有返回false，说明所有的数字都等于root，返回true。
python代码
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def isUnivalTree(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
q=collections.deque()
q.append(root)
val = root.val
while q:
node = q.popleft()
if not node:
continue
if val != node.val:
return False
q.append(node.left)
q.append(node.right)
return True