deques, and lists

双端队列（deque）：与队列类似，也是项的有序集合，有front和rear之分，但是项的加入和移除两端均可而不限于一端。

• Deque() creates a new deque that is empty. It needs no parameters and returns an empty deque.
• addFront(item) adds a new item to the front of the deque. It needs the item and returns nothing.
• addRear(item) adds a new item to the rear of the deque. It needs the item and returns nothing.
• removeFront() removes the front item from the deque. It needs no parameters and returns the item. The deque is modified.
• removeRear() removes the rear item from the deque. It needs no parameters and returns the item. The deque is modified.
• isEmpty() tests to see whether the deque is empty. It needs no parameters and returns a boolean value.
• size() returns the number of items in the deque. It needs no parameters and returns an integer.

python实现：

class Deque:
    def __init__(self):
        self.items = []

    def isEmpty(self):
        return self.items == []

    def addFront(self, item):
        self.items.append(item)

    def addRear(self, item):
        self.items.insert(0,item)

    def removeFront(self):
        return self.items.pop()

    def removeRear(self):
        return self.items.pop(0)

    def size(self):
        return len(self.items)

 例：

列表（list）：抽象数据类型之无序列表

方法：

• List() creates a new list that is empty. It needs no parameters and returns an empty list.
• add(item) adds a new item to the list. It needs the item and returns nothing. Assume the item is not already in the list.
• remove(item) removes the item from the list. It needs the item and modifies the list. Assume the item is present in the list.
• search(item) searches for the item in the list. It needs the item and returns a boolean value.
• isEmpty() tests to see whether the list is empty. It needs no parameters and returns a boolean value.
• size() returns the number of items in the list. It needs no parameters and returns an integer.
• append(item) adds a new item to the end of the list making it the last item in the collection. It needs the item and returns nothing. Assume the item is not already in the list.
• index(item) returns the position of item in the list. It needs the item and returns the index. Assume the item is in the list.
• insert(pos,item) adds a new item to the list at position pos. It needs the item and returns nothing. Assume the item is not already in the list and there are enough existing items to have position pos.
• pop() removes and returns the last item in the list. It needs nothing and returns an item. Assume the list has at least one item.
• pop(pos) removes and returns the item at position pos. It needs the position and returns the item. Assume the item is in the list.

 python实现：

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 UnorderedList:

    def __init__(self):
        self.head = None

    def isEmpty(self):
        return self.head == None

    def add(self,item):
        temp = Node(item)
        temp.setNext(self.head)
        self.head = temp

    def size(self):
        current = self.head
        count = 0
        while current != None:
            count = count + 1
            current = current.getNext()

        return count

    def search(self,item):
        current = self.head
        found = False
        while current != None and not found:
            if current.getData() == item:
                found = True
            else:
                current = current.getNext()

        return found

    def remove(self,item):
        current = self.head
        previous = None
        found = False
        while not found:
            if current.getData() == item:
                found = True
            else:
                previous = current
                current = current.getNext()

        if previous == None:
            self.head = current.getNext()
        else:
            previous.setNext(current.getNext())

列表（list）：抽象数据类型之有序列表

方法：改动了search和add方法

• OrderedList() creates a new ordered list that is empty. It needs no parameters and returns an empty list.
• add(item) adds a new item to the list making sure that the order is preserved. It needs the item and returns nothing. Assume the item is not already in the list.
• remove(item) removes the item from the list. It needs the item and modifies the list. Assume the item is present in the list.
• search(item) searches for the item in the list. It needs the item and returns a boolean value.
• isEmpty() tests to see whether the list is empty. It needs no parameters and returns a boolean value.
• size() returns the number of items in the list. It needs no parameters and returns an integer.
• index(item) returns the position of item in the list. It needs the item and returns the index. Assume the item is in the list.
• pop() removes and returns the last item in the list. It needs nothing and returns an item. Assume the list has at least one item.
• pop(pos) removes and returns the item at position pos. It needs the position and returns the item. Assume the item is in the list

python实现：

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 add(self,item):
        current = self.head
        previous = None
        stop = False
        while current != None and not stop:
            if current.getData() > item:
                stop = True
            else:
                previous = current
                current = current.getNext()
        temp = Node(item)
        if previous == None:
            temp.setNext(self.head)
            self.head = temp
        else:
            temp.setNext(current)
            previous.setNext(temp)
            
    def size(self):
        current = self.head
        count = 0
        while current != None:
            count = count + 1
            current = current.getNext()
        return count
        
    def search(self,item):
        current = self.head
        found = False
        stop = False
        while current != None and not found and not stop:
            if current.getData() == item:
                found = True
            else:
                if current.getData() > item:
                    stop = True
                else:
                    current = current.getNext()
        return found
    
    def remove(self,item):
        current = self.head
        previous = None
        found = False
        while not found:
            if current.getData() == item:
                found = True
            else:
                previous = current
                current = current.getNext()
                
        if previous == None:
            self.head = current.getNext()
        else:
            previous.setNext(current.getNext())