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链表(Linked list)是一种常见的基础数据结构,是一种线性表,但是不像顺序表一样连续存储数据,而是在每一个节点(数据存储单元)里存放下一个节点的位置信息(即地址)。
单向链表图示
""" 算法. 单链表示例: """ class SingleNode(object): """链表的节点类""" def __init__(self, item): # item 表示存放数据的元素 self.item = item # next 下一个节点的标识(地址信息) self.next = None class SingleLinkList(object): """单链表""" def __init__(self, head=None): self.__head = head def is_empty(self): """判断链表是否为空""" return self.__head is None def length(self): """获取链表⻓度""" # cur初始时指向头节点 cur = self.__head # count 表示链表的长度 count = 0 while cur is not None: count += 1 # 将cur后移一个节点 cur = cur.next return count def travel(self): """遍历整个链表""" # cur初始时指向头节点 cur = self.__head while cur is not None: # 打印节点的元素(数值) print(cur.item, end=",") cur = cur.next print() def add(self, item): """链表头部添加元素""" # 创建添加的节点 node = SingleNode(item) # 添加的节点下一个地址指向原来的头部节点地址 # 将新节点的链接域next指向头节点,即__head指向的位置 node.next = self.__head # 将头节点指向添加的节点 self.__head = node def append(self, item): """链表尾部添加元素""" node = SingleNode(item) # 先判断链表是否为空,如果是空则将__head指向新加的节点 if self.is_empty(): self.__head = node # 若不为空,则找到尾部,将尾节点的next指向新节点 else: cur = self.__head while cur.next is not None: cur = cur.next cur.next = node def insert(self, pos, item): """指定位置添加元素""" # 如果pos小于或等于0,就相当于在头部添加节点 if pos <= 0: self.add(item) # 如果pos大于或等于链表的长度,就相当于在尾部添加节点 elif pos >= self.length(): self.append(item) # 找到指定位置 else: # cur = self.__head # count相当于索引 node = SingleNode(item) count = 0 # per用于指向指定位置pos的前一个位置pos-1,初始从头节点开始定位置 pre = self.__head while count < (pos - 1): count += 1 pre = pre.next # 先将新节点node的next指向插入位置的节点 node.next = pre.next # 将插入位置的前一个节点的next指向新节点node pre.next = node def remove(self, item): """删除节点""" cur = self.__head pre = None while cur is not None: # 找到这个元素 if cur.item == item: # 第一个就是要删除的元素 if not pre: # 将头节点指向删除节点的下一个节点位置 self.__head = cur.next # 找到删除位置的上一个节点next指向删除位置的下一个节点位置 else: pre.next = cur.next break else: # 继续按链表后移节点 pre = cur cur = cur.next def search(self, item): """查找节点是否存在""" cur = self.__head while cur is not None: if cur.item == item: return True cur = cur.next return False if __name__ == "__main__": lb = SingleLinkList() print(lb.is_empty()) lb.append(8) lb.add(6) lb.add(6) lb.insert(2, 9) lb.travel() lb.add(3) print(lb.length()) print(lb.search(5)) lb.remove(6) lb.travel()
一种更复杂的链表是“双向链表”或“双面链表”。每个节点有两个链接:一个指向前一个节点,当此节点为第一个节点时,指向空值;而另一个指向下一个节点,当此节点为最后一个节点时,指向空值。
class Node(object): """双向链表节点""" def __init__(self, item): self.item = item self.next = None self.prev = None class DLinkList(object): """双向链表""" def __init__(self): self.__head = None def is_empty(self): """判断链表是否为空""" return self.__head == None def length(self): """返回链表的长度""" cur = self.__head count = 0 while cur != None: count += 1 cur = cur.next return count def travel(self): """遍历链表""" cur = self.__head while cur != None: print cur.item, cur = cur.next print "" def add(self, item): """头部插入元素""" node = Node(item) if self.is_empty(): # 如果是空链表,将_head指向node self.__head = node else: # 将node的next指向_head的头节点 node.next = self.__head # 将_head的头节点的prev指向node self.__head.prev = node # 将_head 指向node self.__head = node def append(self, item): """尾部插入元素""" node = Node(item) if self.is_empty(): # 如果是空链表,将_head指向node self.__head = node else: # 移动到链表尾部 cur = self.__head while cur.next != None: cur = cur.next # 将尾节点cur的next指向node cur.next = node # 将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
指定位置插入节点
def insert(self, pos, item): """在指定位置添加节点""" if pos <= 0: self.add(item) elif pos > (self.length()-1): self.append(item) else: node = Node(item) cur = self.__head count = 0 # 移动到指定位置的前一个位置 while count < (pos-1): count += 1 cur = cur.next # 将node的prev指向cur node.prev = cur # 将node的next指向cur的下一个节点 node.next = cur.next # 将cur的下一个节点的prev指向node cur.next.prev = node # 将cur的next指向node cur.next = node
删除元素
def remove(self, item): """删除元素""" cur = self.__head while cur != None: # 找到了要删除的元素 if cur.item == item: # 先判断此结点是否是头节点 # 头节点 if cur == self.__head: self.__head = cur.next # 如果存在下一个结点,则设置下一个结点 if cur.next: # 判断链表是否只有一个结点 cur.next.prev = None else: cur.prev.next = cur.next # 如果存在下一个结点,则设置下一个结点 if cur.next: cur.next.prev = cur.prev break else: cur = cur.next
测试
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()
单链表的一个变形是单向循环链表,链表中最后一个节点的next域不再为None,而是指向链表的头节点。
class Node(object): """节点""" def __init__(self, item): self.item = item self.next = None class SinCycLinkedlist(object): """单向循环链表""" def __init__(self): self.__head = None def is_empty(self): """判断链表是否为空""" return self.__head == None def length(self): """返回链表的长度""" # 如果链表为空,返回长度0 if self.is_empty(): return 0 count = 1 cur = self.__head while cur.next != self.__head: count += 1 cur = cur.next return count def travel(self): """遍历链表""" if self.is_empty(): return cur = self.__head print cur.item, while cur.next != self.__head: cur = cur.next print cur.item, print "" def add(self, item): """头部添加节点""" node = Node(item) if self.is_empty(): self.__head = node node.next = self.__head else: #添加的节点指向_head node.next = self.__head # 移到链表尾部,将尾部节点的next指向node cur = self.__head while cur.next != self.__head: cur = cur.next cur.next = node #_head指向添加node的 self.__head = node def append(self, item): """尾部添加节点""" node = Node(item) if self.is_empty(): self.__head = node node.next = self.__head else: # 移到链表尾部 cur = self.__head while cur.next != self.__head: cur = cur.next # 将尾节点指向node cur.next = node # 将node指向头节点_head node.next = self.__head def insert(self, pos, item): """在指定位置添加节点""" if pos <= 0: self.add(item) elif pos > (self.length()-1): self.append(item) else: node = Node(item) cur = self.__head count = 0 # 移动到指定位置的前一个位置 while count < (pos-1): count += 1 cur = cur.next node.next = cur.next cur.next = node def remove(self, item): """删除一个节点""" # 若链表为空,则直接返回 if self.is_empty(): return # 将cur指向头节点 cur = self.__head pre = None while cur.next != self.__head: if cur.item == item: # 先判断此结点是否是头节点 if cur == self.__head: # 头节点的情况 # 找尾节点 rear = self.__head while rear.next != self.__head: rear = rear.next self.__head = cur.next rear.next = self.__head else: # 中间节点 pre.next = cur.next return else: pre = cur cur = cur.next # 退出循环,cur指向尾节点 if cur.item == item: if cur == self.__head: # 链表只有一个节点 self.__head = None else: # pre.next = cur.next pre.next = self.__head def search(self, item): """查找节点是否存在""" if self.is_empty(): return False cur = self.__head if cur.item == item: return True while cur.next != self.__head: cur = cur.next if cur.item == item: return True return False if __name__ == "__main__": ll = SinCycLinkedlist() 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(7) ll.remove(1) print "length:",ll.length() ll.travel()
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