Python 雙向鏈表

操作

• is_empty() 鏈表是否為空
• length() 鏈表長度
• travel() 遍歷鏈表
• add(item) 鏈表頭部添加
• append(item) 鏈表尾部添加
• insert(pos, item) 指定位置添加
• remove(item) 刪除節點
• search(item) 查找節點是否存在

class Node(object):
    """雙向鏈表節點"""
    def __init__(self, item):
        self.item = item
        self.next = None
        self.prev = None


class DLinkList(object):
    """雙向鏈表"""
    def __init__(self):
        self._head = None

    def is_empty(self):
        """判斷鏈表是否為空"""
        return self._head == None

    def length(self):
        """返回鏈表的長度"""
        cur = self._head
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍歷鏈表"""
        cur = self._head
        while cur != None:
            print cur.item,
            cur = cur.next
        print ""

    def add(self, item):
        """頭部插入元素"""
        node = Node(item)
        if self.is_empty():
            # 如果是空鏈表，將_head指向node
            self._head = node
        else:
            # 將node的next指向_head的頭節點
            node.next = self._head
            # 將_head的頭節點的prev指向node
            self._head.prev = node
            # 將_head 指向node
            self._head = node

    def append(self, item):
        """尾部插入元素"""
        node = Node(item)
        if self.is_empty():
            # 如果是空鏈表，將_head指向node
            self._head = node
        else:
            # 移動到鏈表尾部
            cur = self._head
            while cur.next != None:
                cur = cur.next
            # 將尾節點cur的next指向node
            cur.next = node
            # 將node的prev指向cur
            node.prev = cur



    def search(self, item):
        """查找元素是否存在"""
        cur = self._head
        while cur != None:
            if cur.item == item:
                return True
            cur = cur.next
        return False

def insert(self, pos, item):
        """在指定位置添加節點"""
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            node = Node(item)
            cur = self._head
            count = 0
            # 移動到指定位置的前一個位置
            while count < (pos-1):
                count += 1
                cur = cur.next
            # 將node的prev指向cur
            node.prev = cur
            # 將node的next指向cur的下一個節點
            node.next = cur.next
            # 將cur的下一個節點的prev指向node
            cur.next.prev = node
            # 將cur的next指向node
            cur.next = node

def remove(self, item):
        """刪除元素"""
        if self.is_empty():
            return
        else:
            cur = self._head
            if cur.item == item:
                # 如果首節點的元素即是要刪除的元素
                if cur.next == None:
                    # 如果鏈表只有這一個節點
                    self._head = None
                else:
                    # 將第二個節點的prev設置為None
                    cur.next.prev = None
                    # 將_head指向第二個節點
                    self._head = cur.next
                return
            while cur != None:
                if cur.item == item:
                    # 將cur的前一個節點的next指向cur的后一個節點
                    cur.prev.next = cur.next
                    # 將cur的后一個節點的prev指向cur的前一個節點
                    cur.next.prev = cur.prev
                    break
                cur = cur.next

if __name__ == "__main__":
    ll = DLinkList()
    ll.add(1)
    ll.add(2)
    ll.append(3)
    ll.insert(2, 4)
    ll.insert(4, 5)
    ll.insert(0, 6)
    print "length:",ll.length()
    ll.travel()
    print ll.search(3)
    print ll.search(4)
    ll.remove(1)
    print "length:",ll.length()
    ll.travel()