What does this function do? Assume that for any node, node.item will be less than or equal to all items in node.link. [2.5 marks]

State and explain the best case complexity of this function [2.5 marks]

def mystery(node1: Node[int], node2: Node[int]):
    if node1 is None: 
        return node2
    if node2 is None:
        return node1
    if node1.item <= node2.item:
        node1.link = mystery(node1.link, node2)
        return node1
    else:
        node2.link = mystery(node1, node2.link)
        return node2