swapnodes.py

class LL:
    @classmethod
    def from_list(cls, vals):
        if not vals:
            raise "LL must have at least one element"
        root = cls(vals[0])
        cur = root
        for val in vals[1:]:
            cur.next = cls(val)
            cur = cur.next
        return root


    def __init__(self, val, next=None):
        self.val = val
        self.next = next

    def __repr__(self):
        return f'<LL: val={self.val} next={self.next}>'

    def print(self):
        head = self
        l = []
        while head:
            l.append(head.val)
            head = head.next
        print(l)


def swap_nodes(ll, k):
    root = ll

    a = None
    len = 1
    while ll.next:
        if len == k:
            a = ll
        len +=1
        ll = ll.next
    
    b = root
    for _ in range(len - k):
        b = b.next

    a.val, b.val = b.val, a.val


ll = LL.from_list([1, 2, 3, 4, 5])
ll.print()
swap_nodes(ll, 2)
ll.print()