有序List

• 有序列表是指列表中的元素是有顺序的，例如从小到大或者从大到小的顺序。
• OrderedList()：创建一个新的有序表
• add(item)：添加元素
• remove(item)：删除item元素
• search(item)：查看item是否在有序表中，返回一个布尔值
• isEmpty()： 返回一个布尔值，判断有序表是否为空
• size()：返回有序表的长度，即元素的个数
• index(item)：返回元素item的索引值
• pop()：删除最后的元素
• pop(pos)：删除指定位置的元素

class Node:
    def __init__(self, initdata):
        self.data = initdata
        self.next = None
    def getData(self):
        return self.data
    def getNext(self):
        return self.next
    def setData(self, newdata):
        self.data = newdata
    def setNext(self,newNext):
        self.next = newNext

class OrderedList:
    def __init__(self):
        self.head = None
    
    def isEmpty(self):
        return self.head == None
        
    def size(self):
        count = 0
        current = self.head
        while current != None:
            current = current.getNext()
            count += 1
        return count
    
    def remove(self, item):
        current = self.head
        previous = None
        found = False
        while not found and current != None:
            if current.getData() == item:
                found = True
            else:
                previous = current
                current = current.getNext()
        
        if previous == None:
            self.head = current.getNext()
        else:
            previous.setNext(current.getNext())
            
    def add(self, item):
        '''和无序表不同'''
        temp = Node(item)
        
        previous = None
        current = self.head
        stop = False
        
        while current != None and not stop:
            if current.getData() > item:
                stop = True
            else:
                previous = current
                current = current.getNext()
                     
        if previous == None:
            temp.setNext(self.head)
            self.head = temp
        else:
            temp.setNext(current)
            previous.setNext(temp)      
            
    def search(self, item):
        '''和无序表不同，引入了提前终止条件(列表是升序)'''
        current = self.head
        stop = False
        found = False
        while not found and current != None and not stop:
            if current.getData() == item:
                found = True
            else:
                if current.getData() < item:
                    current = current.getNext()
                else:
                    stop = True
        return found
    
    def pop(self, pos=None):
        if self.isEmpty():
            print("list is empty")
        elif pos == None:
                current = self.head
                previous = None
                pre_previous = None
            
                while current != None:
                    pre_previous = previous
                    previous = current
                    current = current.getNext()
                pre_previous.setNext(current)
        else:
            current = self.head
            previous = None
            for i in range(pos):
                previous = current
                current = current.getNext()
            previous.setNext(current.getNext())
        
            
    def index(self, item):
        current = self.head
        count = 0
        found = False
        while not found and current != None:
            if current.getData() == item:
                found = True
            else:
                current = current.getNext()
                count += 1
        return count
    
    

mylist = OrderedList()
mylist.add(31)
mylist.add(77)
mylist.add(17)
mylist.add(93)
mylist.add(26)
mylist.add(54)

print(mylist.index(77))
print(mylist.size())
print(mylist.search(93))
print(mylist.search(31))

mylist.pop(pos=2)
print(mylist.search(31))
# mylist.remove(17)
print(mylist.size())
mylist.pop()
print(mylist.size())

4
6
True
True
False
5
4

m = OrderedList()
m.pop()

list is empty

• 说明：上述方法中index()、pop()等是自己编写，自己目前检查没错，也可能存在一些特殊的例子，若有错误，欢迎指正！
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