Leetcode 94 Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree

{1,#,2,3}

,

1
\
2
/
3

return

[1,3,2]

.

Note: Recursive solution is trivial, could you do it iteratively?

def inorder_traversal(root)
ans, stack = [], [[false,root]]
while not stack.empty?
visit, node = stack.pop
if node
stack << [false,node.right] << [true,node] << [false,node.left] if not visit
ans << node.val if visit
end
end
ans
end