查找列表中的下一个元素

def get_next_element(arr, index):
    if index < len(arr) - 1:
        return arr[index + 1]
    else:
        return None  # 或者抛出异常

# 示例
arr = [1, 2, 3, 4, 5]
print(get_next_element(arr, 3))  # 输出 5
print(get_next_element(arr, 4))  # 输出 None

class ListNode:
    def __init__(self, value=0, next=None):
        self.value = value
        self.next = next

def get_next_element(head, current):
    if not head or not current or not current.next:
        return None  # 或者抛出异常
    return current.next.value

# 示例
head = ListNode(1, ListNode(2, ListNode(3)))
print(get_next_element(head, head))  # 输出 2
print(get_next_element(head, head.next.next))  # 输出 None