用于旋转链表的Python程序

给定一个单链表，将链表逆时针旋转 k 个节点。其中 k 是给定的正整数。例如，如果给定的链表是 10->20->30->40->50->60，k 为 4，则链表应修改为 50->60->10->20->30- >40。假设 k 小于链表中的节点数。

方法一：
要旋转链表，我们需要将第 k 个节点的 next 更改为 NULL，将最后一个节点的 next 更改为前一个 head 节点，最后将 head 更改为第 (k+1) 个节点。所以我们需要掌握三个节点：第k个节点、第(k+1)个节点和最后一个节点。
从头开始遍历列表并在第 k 个节点处停止。存储指向第 k 个节点的指针。我们可以使用 kthNode->next 获得第 (k+1) 个节点。继续遍历直到结束并存储指向最后一个节点的指针。最后，如上所述更改指针。

下图显示了如何在代码中使用旋转函数：

Python

# Python program to rotate 
# a linked list
# Node class 
class Node:
  
    # Constructor to initialize 
    # the node object
    def __init__(self, data):
        self.data = data
        self.next = None
  
class LinkedList:
  
    # Function to initialize head
    def __init__(self):
        self.head = None
  
    # Function to insert a new node
    # at the beginning
    def push(self, new_data):
        # allocate node and put the data
        new_node = Node(new_data)
  
        # Make next of new node as head
        new_node.next = self.head
          
        # Move the head to point to the 
        # new Node
        self.head = new_node
  
    # Utility function to print it the 
    # linked LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next
  
    # This function rotates a linked list 
    # counter-clockwise and updates the 
    # head. The function assumes that k 
    # is smaller than size of linked list. 
    # It doesn't modify the list if k is 
    # greater than of equal to size
    def rotate(self, k):
        if k == 0: 
            return 
          
        # Let us understand the below code 
        # for example k = 4 and list = 
        # 10->20->30->40->50->60
        current = self.head
          
        # current will either point to kth 
        # or NULL after this loop current 
        # will point to node 40 in the above 
        # example
        count = 1 
        while(count 20->30->40->50->60
for i in range(60, 0, -10):
    llist.push(i)
  
print "Given linked list"
llist.printList()
llist.rotate(4)
  
print "Rotated Linked list"
llist.printList()
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

Python3

# Python3 program to rotate a 
# linked list counter clock wise
   
# Link list node 
class Node:
      
    def __init__(self):
          
        self.data = 0
        self.next = None
  
# This function rotates a linked list
# counter-clockwise and updates the
# head. The function assumes that k is
# smaller than size of linked list.
def rotate(head_ref, k):
  
    if (k == 0):
        return
   
    # Let us understand the below
    # code for example k = 4 and
    # list = 10.20.30.40.50.60.
    current = head_ref
   
    # Traverse till the end.
    while (current.next != None):
        current = current.next
   
    current.next = head_ref
    current = head_ref
      
    # Traverse the linked list to k-1 
    # position which will be last 
    # element for rotated array.
    for i in range(k - 1):
        current = current.next
   
    # Update the head_ref and last 
    # element pointer to None
    head_ref = current.next
    current.next = None
    return head_ref
   
# UTILITY FUNCTIONS 
# Function to push a node 
def push(head_ref, new_data):
  
    # Allocate node 
    new_node = Node()
   
    # Put in the data 
    new_node.data = new_data
   
    # Link the old list off 
    # the new node 
    new_node.next = (head_ref)
   
    # Move the head to point
    # to the new node 
    (head_ref) = new_node
    return head_ref
      
# Function to print linked list 
def printList(node):
  
    while (node != None):
        print(node.data, end = ' ')
        node = node.next
  
# Driver code
if __name__=='__main__':
      
    # Start with the empty list 
    head = None
   
    # Create a list 
    # 10.20.30.40.50.60
    for i in range(60, 0, -10):
        head = push(head, i)
   
    print("Given linked list ")
    printList(head)
    head = rotate(head, 4)
   
    print("\nRotated Linked list ")
    printList(head)
# This code is contributed by rutvik_56
Output:Given linked list 
10 20 30 40 50 60 
Rotated Linked list 
50 60 10 20 30 40Please refer complete article on Rotate a Linked List for more details!

p>输出：

Given linked list
10  20  30  40  50  60
Rotated Linked list
50  60  10  20  30  40

方法二：
要将链表旋转k，我们可以先使链表循环，然后从头节点向前移动k-1步，使第(k-1)个节点的next为空，并以第k个节点为头。

Python3

# Python3 program to rotate a 
# linked list counter clock wise
   
# Link list node 
class Node:
      
    def __init__(self):
          
        self.data = 0
        self.next = None
  
# This function rotates a linked list
# counter-clockwise and updates the
# head. The function assumes that k is
# smaller than size of linked list.
def rotate(head_ref, k):
  
    if (k == 0):
        return
   
    # Let us understand the below
    # code for example k = 4 and
    # list = 10.20.30.40.50.60.
    current = head_ref
   
    # Traverse till the end.
    while (current.next != None):
        current = current.next
   
    current.next = head_ref
    current = head_ref
      
    # Traverse the linked list to k-1 
    # position which will be last 
    # element for rotated array.
    for i in range(k - 1):
        current = current.next
   
    # Update the head_ref and last 
    # element pointer to None
    head_ref = current.next
    current.next = None
    return head_ref
   
# UTILITY FUNCTIONS 
# Function to push a node 
def push(head_ref, new_data):
  
    # Allocate node 
    new_node = Node()
   
    # Put in the data 
    new_node.data = new_data
   
    # Link the old list off 
    # the new node 
    new_node.next = (head_ref)
   
    # Move the head to point
    # to the new node 
    (head_ref) = new_node
    return head_ref
      
# Function to print linked list 
def printList(node):
  
    while (node != None):
        print(node.data, end = ' ')
        node = node.next
  
# Driver code
if __name__=='__main__':
      
    # Start with the empty list 
    head = None
   
    # Create a list 
    # 10.20.30.40.50.60
    for i in range(60, 0, -10):
        head = push(head, i)
   
    print("Given linked list ")
    printList(head)
    head = rotate(head, 4)
   
    print("\nRotated Linked list ")
    printList(head)
# This code is contributed by rutvik_56

输出：

Given linked list 
10 20 30 40 50 60 
Rotated Linked list 
50 60 10 20 30 40

有关详细信息，请参阅有关旋转链接列表的完整文章！

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