TheAlgorithms-Ruby/data_structures/binary_trees/inorder_traversal.rb

# 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 {Integer[]}
def inorder_traversal(root)
    ans = []
    def traverse(node, ans)
        if node != nil
            traverse(node.left, ans)
            ans.push(node.val)
            traverse(node.right,ans)
        end
    end
    traverse(root,ans)
    return ans
end