18-1在O(1)时间删除链表结点

给定单向链表的头指针和一个结点指针，定义一个函数在O(1)时间删除该结点。

class Node:
    def __init__(self, val, nxt=None):
        self.value = val
        self.next = nxt

class Node_list:
    def __init__(self, begin=None):
        self.begin = begin

def delete_node(lyst, aim_node):
    if lyst is None or lyst.begin is None or lyst.begin.value is None or \
            aim_node is None or aim_node.value is None:
        return 'Wrong!'
    # begin
    if lyst.begin is aim_node:
        lyst.begin = lyst.begin.next
        return 'Success'
    # middle
    elif aim_node.next:
        aim_node.value = aim_node.next.value
        aim_node.next = aim_node.next.next
        return 'Success'
    # end
    else:
        probe = lyst.begin
        while probe:
            if probe is aim_node:
                probe.next = None
                return 'Success'
            probe = probe.next
        

if __name__ == '__main__':
    a = Node('a')
    b = Node('b', a)
    c = Node('c', b)
    d = Node('d', c)
    void = Node(None)
    lyst = Node_list(d)
    lyst_void = Node_list(void)

    assert delete_node(lyst, c) == 'Success'
    assert delete_node(lyst, d) == 'Success'
    assert delete_node(lyst, a) == 'Success'
    assert delete_node(None, None) == 'Wrong!'
    
    assert delete_node(lyst_void, c) == 'Wrong!'
    assert delete_node(lyst, void) == 'Wrong!'