Python 链表-插入方法

Question

我对 DataStructure 有点陌生，我试图编写 LinkedList，但我无法弄清楚为什么我的插入方法不起作用。 如果您有任何改进建议，请写信给我

class Node:
    def __init__(self, data):
        self.item = data
        self.ref = None


class LinkedList:
    def __init__(self):
        self.start_node = None
        self.index = 0

    def append(self, val):
        new = Node(val)

        if not self.start_node:
            self.start_node = new
            return

        last = self.start_node
        while last.ref:
            last = last.ref
        last.ref = new

        self.index += 1

    def insert(self, index, value):
        start_counting = 0
        start = self.start_node

        while start_counting < index:
            start = start.ref
            start_counting += 1

        NewNode = Node(value)
        tmp = start.ref
        start = NewNode
        start.ref = tmp

    def display(self):
        ls = []
        last = self.start_node
        while last:
            ls.append(last.item)
            last = last.ref
        return ls

Answer 1

插入 function 正在替换当前节点而不是链接它。 我将用一个例子来说明这一点：

我有这个链表：1 -> 2 -> 3 我想在 position 1 中插入一个元素“4”（position 1 中的当前数字是 2）。 迭代将是：

start_counting = 0
start = self.start_node (node with value 1)

---

第一次迭代：

start_counting < 1 -> true

start = start.ref (node with value 2)
start_counting += 1 (actual count 1)

第二次迭代：

start_counting < 1 -> false

start = (node with value 2)

---

之后代码继续如下：

We create the new Node (4 in my example) and we do:

tmp = start.ref (which is 3)
start = NewNode (we are replacing the node completely, we are not linking the node with another) <- here is the error
start.ref = tmp (which in this case is 3)

---

要修复错误，您应该考虑两件事：

1. 迭代直到前一个节点，而不是直到下一个节点。
2. 处理要插入一个节点作为链表头的情况，换句话说，在 position 0 中。

代码将类似于：

    def insert(self, index, value):
        start_counting = 0
        start = self.start_node
        NewNode = Node(value)

        if index == 0: # Handling the position 0 case.
            NewNode.ref = start
            self.start_node = NewNode
        else:
            while start_counting < index - 1: # Iterating until the previous node.
                start_counting += 1
                start = start.ref

            NewNode.ref = start.ref
            start.ref = NewNode

使用以下代码进行了测试，并且可以正常工作：

a = LinkedList()
a.append(1)
a.append(2)
a.append(3)
a.insert(0, 4)
a.insert(1, 5)
print(a.display())

Answer 2

链表没有索引，所以不需要从 index=0 开始。 同样对于链表，有 3 种插入方法，insert_to_first、insert_to_last 或 insert_to_any_position。 您正在实施 insert_to_any position。

def insert(self, index, value):
    start_counting = 0
    start = self.start_node

    while start_counting < index:
        start = start.ref
        start_counting += 1
    # so far no issue
    NewNode = Node(value,None) # new Node accepts 2 args
    # Let's write a linked list to visualize
    # A->B->C-> adding_Node_Here ->D->E... make sure we dont lose ref to D when we inser
    # after while loop, we end up start=C
    NewNode.ref=start.ref # we keep the ref to D
    start.ref=NewNode # now C refs to NewNode
    self.index+=1 # again linked list is not indexed. "size" is better term