python精选例题笔记（每日一练）—— 创建链表的类 create class LinkedList

1.题目
(1)Create class Linked List (Unordered)
(2)Create class Linked List (ordered)

List of operations a link list should supported:

1.Initialize (empty/from list)
2.isEmpty
3.add(val)
4.remove(val)
5.__ str __
6.__ repr __
7.index
8.__ contains __
9.insert(idx, val)
10.len
(Code to be completed in class)

2.解题思路
先实现简单的function，再研究较难的function。

function实现顺序：
Initialize -> __ str __ -> __ repr __ -> isEmpty -> index -> __ contains __ -> len -> add -> remove(较难) -> insert (较难)

对于有序链表，需要修改函数 add() 和 insert()。

3.code：
(1)创建结点

#define Node
class Node():
    def __init__(self, val, nxt):
        self.val = val
        self.next = nxt
    def __str__(self):
        return str(self.val)
    def __repr__(self):
        return 'Node(' + str(self.val) + ')'

(2)创建class LinkedList

class LinkedList():
    def __init__(self, lst = None):
        self.head = None
        if lst != None:
            for val in lst:
                self.add(val)
                
    def add(self, val):
        self.head = Node(val, self.head)
        
    def remove(self, val):
        p = self.head
        # if list is None, do nothing
        if p == None:
            return
        # if the first val need to remove
        if p.val == val:
            self.head = p.next
        while p.next != None and p.next.val != val:
            p = p.next
        if p.next != None:
            p.next = p.next.next
        # if the val is not included in the list，do nothing
        
    def index(self, val):
        p = self.head
        idx = 0
        while p != None:
            if p.val == val:
                return idx
            idx += 1
            p = p.next
            
        return -1 # not find
            
    def insert(self, idx, val):
        # idx = 0 or list is empty
        if idx == 0 or self.head == None:
            self.add(val)
        # if idx is larger than length,insert at the end of the list
        elif idx > len(self):
            p = self.head
            while p != None:
                p = p.next
            p.next = Node(val, None)
        else:
            p = self.head
            while p != None and idx > 1:
                p = p.next
                idx -= 1
            p.next = Node(val, p.next)
            
    def isEmpty(self):
        return self.head == None
    
    def __contains__(self, val):
        return self.index(val) != -1
    
    def __len__(self):
        p = self.head
        l = 0
        while p != None:
            l += 1
            p = p.next
        return l
    
    def __str__(self):
        p = self.head
        s = '->'
        while p != None:
            s += str(p.val) + '->'
            p = p.next
        s += 'None'
        return s
    
    def __repr__(self):
        return 'LinkedList(' + str(self) + ')'

(3)创建 class OrderedLinkedList

class OrderedLinkedList(LinkedList):
    def add(self, val):
        p = self.head
        if not p:
            self.head = Node(val, None)
        elif val < p.val:
            self.head = Node(val, p)
        else:
            while p != None and p.next.val < val:
                p = p.next
            p.next = Node(val, p.next)
            
    def insert(self, idx, val):
        #ignore idx
        self.add(val)

测试代码

ol = OrderedLinkedList([5,3,1,4])
print(ol)
ol.add(2)
print(ol)
ol.remove(3)
print(ol)

结果
->1->3->4->5->None
->1->2->3->4->5->None
->1->2->4->5->None