invert-binary-tree.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 {TreeNode}
def invert_tree(root)
    return root if root.nil?
    s=[]
    s.push(root)
    
    until s.empty?
        r = s.pop
        tmp = r.left
        r.left=r.right
        r.right=tmp
        
        s.push r.left unless r.left.nil?
        s.push r.right unless r.right.nil?
    end
    return root
end