数据结构与算法笔记(5) - 双链表

双链表，节点之间具有双向链接，即在每个节点都有前和后两个指针，分别指向前一个节点和后一个节点。

节点类:

class Node(object):
    def __init__(self, elem, next_=None, prev=None):
        self.elem = elem
        self.next = next_
        self.prev = prev

双链表：

class LinkedList(object):

    def __init__(self):
        self.head = None
        
    def is_empty(self):
        return self.head is None

    def length(self):
        """链表长度"""
        count = 0
        pointer = self.head
        while pointer is not None:
            pointer = pointer.next
            count += 1
        return counter

    def search(self, elem):
        """搜索"""
        if self.is_empty():
            return -1
        p = self.head
        while p is not None:
            if p.elem == elem:
                return p.elem
            p = p.next
        return -1

    def add(self, elem):
        """首部插入"""
        node = Node(elem)
        if self.is_empty():
            self.head = node
        else:
            node.next = self.head
            self.head.prev = node
            self.head = node

    def append(self, elem):
        """尾部插入"""
        node = Node(elem)
        if self.is_empty():
            self.head = node
        else:
            p = self.head
            while p.next:
                p = p.next
            p.next = node
            node.next = p

    def insert(self, pos):
        """一般位置插入"""
        if pos <= 0:
            self.add(elem)
        elif pos > self.length():
            self.append(elem)
        else:
            node = Node(elem)
            idx = 0
            p = self.head
            while idx <= pos - 1:
                idx += 1
                p = p.next
            node.next = p.next
            p.next.prev = node
            node.prev = p
            p.next = node

    def pop(self):
        """弹出尾部元素"""
        if self.is_empty():
            return -1
        p = self.head
        while p.next:
            p = p.next
        elem = p.next.elem
        p.next.prev = None
        p.next = None
        return elem
    
    def pop_first(self):
        """弹出第一个节点"""
        if self.is_empty():
            return -1
        if not self.head.next:
            elem = self.head.elem
            self.head = None
            return elem
        else:
            elem = self.head.elem
            p = self.head.next
            p.prev = None
            self.head.next = None
            self.head = p
            return elem

    def delete(self, pos):
        """删除指定节点"""
        if pos <= 0:
            return self.pop_first()
        if pos >= self.length() - 1:
            return self.pop()
        p = self.head
        idx = 0
        while idx <= pos-1:
            idx += 1
            p = p.next
        p.prev.next = p.next
        p.next.prev = p.prev
        p.next = None
        p.prev = None

    def travel(self):
        """遍历"""
        p = self.head
        while p:
            print(p.elem)
            p = p.next

    def reverse(self):
        """反转"""
        if self.is_empty():
            return -1
        p = self.head
        while p:
            p_next = p.next
            p.next = p.prev
            p.prev = p_next
            p = p_next
            if p:
                self.head = p

    def sort(self):
        """排序
        采用插入排序算法，交换指针
        """
        if self.is_empty():
            return -1
        if not self.head.next:
            return -1
        p_prev = self.head
        p = p_prev.next
        p_prev.next = None
        while p:
            h = self.head
            q = None
            while h and h.elem <= p.elem:
                q = h
                h = h.next
            p_next = p.next
            p.next = h
            p.prev = q
            if q is not None:
                q.next = p
            else:
                self.head = p
            p = p_next