# Definition for a binary tree node.

class TreeNode

attr_accessor :val, :left, :right

def initialize(val)

@val = val

@left, @right = nil, nil

end

end

# @param {TreeNode} root

# @return {Boolean}

def is_symmetric(root)

if root.nil?

return true

end

if root.left.nil? and root.right.nil?

return true

end

leftVector = []

rightVector = []

collect_left root.left, leftVector

collect_right root.right, rightVector

if leftVector.size != rightVector.size

return false

end

index = 0

bound = leftVector.size

while index < bound and leftVector[index] == rightVector[index]

index += 1

end

if index != bound

false

else

true

end

end

def collect_left(node, vector)

if node.nil?

vector << '#'

return

end

vector << node.val

collect_left node.left, vector

collect_left node.right, vector

end

def collect_right(node, vector)

if node.nil?

vector << '#'

return

end

vector << node.val

collect_right node.right, vector

collect_right node.left, vector

end