用于重新排列链接列表的Python程序，以使所有偶数和奇数定位的节点都在一起

重新排列链表，使所有奇数位置节点在一起，所有偶数位置节点在一起，
例子：

Input:   1->2->3->4
Output:  1->3->2->4

Input:   10->22->30->43->56->70
Output:  10->30->56->22->43->70

这个问题的重要一点是确保处理以下所有情况

1. 空链表。
2. 只有一个节点的链表。
3. 只有两个节点的链表。
4. 具有奇数个节点的链表。
5. 具有偶数个节点的链表。

下面的程序分别为奇数和偶数位置的当前节点维护两个指针“奇数”和“偶数”。我们还存储偶数链表的第一个节点，以便在所有奇数和偶数节点在两个不同的链表中连接在一起之后，我们可以将偶数链表附加到奇数链表的末尾。

Python3

# Python3 program to rearrange a 
# linked list in such a way that 
# all odd positioned node are stored 
# before all even positioned nodes 
  
# Linked List Node 
class Node: 
    def __init__(self, d):
        self.data = d
        self.next = None
  
class LinkedList:
    def __init__(self):
        self.head = None
          
    # A utility function to create
    # a new node 
    def newNode(self, key): 
        temp = Node(key) 
        self.next = None
        return temp 
  
    # Rearranges given linked list 
    # such that all even positioned 
    # nodes are before odd positioned. 
    # Returns new head of linked List. 
    def rearrangeEvenOdd(self, head): 
          
        # Corner case 
        if (self.head == None): 
            return None
  
        # Initialize first nodes of 
        # even and odd lists 
        odd = self.head 
        even = self.head.next
  
        # Remember the first node of 
        # even list so that we can 
        # connect the even list at the 
        # end of odd list. 
        evenFirst = even 
  
        while (1 == 1): 
              
            # If there are no more nodes, 
            # then connect first node of even 
            # list to the last node of odd list 
            if (odd == None or even == None or 
               (even.next) == None): 
                odd.next = evenFirst 
                break
  
            # Connecting odd nodes 
            odd.next = even.next
            odd = even.next
  
            # If there are NO more even nodes 
            # after current odd. 
            if (odd.next == None): 
                even.next = None
                odd.next = evenFirst 
                break
  
            # Connecting even nodes 
            even.next = odd.next
            even = odd.next
        return head
  
    # A utility function to print a 
    # linked list 
    def printlist(self, node): 
        while (node != None): 
            print(node.data, end = "")
            print("->", end = "")
            node = node.next
        print ("NULL")
          
    # Function to insert a new node 
    # at the beginning 
    def push(self, new_data): 
        new_node = Node(new_data) 
        new_node.next = self.head 
        self.head = new_node
  
# Driver code 
ll = LinkedList()
ll.push(5)
ll.push(4)
ll.push(3)
ll.push(2)
ll.push(1)
print ("Given Linked List")
ll.printlist(ll.head) 
  
start = ll.rearrangeEvenOdd(ll.head) 
  
print ("Modified Linked List")
ll.printlist(start)
# This code is contributed by Prerna Saini

输出：

Given Linked List
1->2->3->4->5->NULL
Modified Linked List
1->3->5->2->4->NULL

请参阅有关重新排列链表的完整文章，以便所有偶数和奇数位置的节点都在一起以获取更多详细信息！