Python implementation code example for single-chain table inversion, single-chain python

Python implementation code example for single-chain table inversion, single-chain python

You can use cycles or recursion to reverse a single-chain table.

1. Cyclic inversion of a single-chain table

In the cyclic method, pre is used to point to the forward node, and cur points to the current node. You can point cur-> next to pre each time.

Code:

Class ListNode: def _ init _ (self, x): self. val = x; self. next = None; def nonrecurse (head): # The loop method reverses the linked list if head is None or head. next is None: return head; pre = None; cur = head; h = head; while cur: h = cur; tmp = cur. next; cur. next = pre; pre = cur; cur = tmp; return h; head = ListNode (1); # test code p1 = ListNode (2 ); # create a linked list 1-> 2-> 3-> 4-> None; p2 = ListNode (3); p3 = ListNode (4); head. next = p1; p1.next = p2; p2.next = p3; p = nonrecurse (head); # output chain table 4-> 3-> 2-> 1-> None while p: print p. val; p = p. next;

Result:

4
3
2
1
>>>

2. Recursive single-chain table Inversion

Class ListNode: def _ init _ (self, x): self. val = x; self. next = None; def recurse (head, newhead): # recursion, head is the head node of the original linked list, newhead is the head node of the reverse linked list if head is None: return; if head. next is None: newhead = head; else: newhead = recurse (head. next, newhead); head. next. next = head; head. next = None; return newhead; head = ListNode (1); # test code p1 = ListNode (2 ); # create a linked list 1-> 2-> 3-> 4-> None p2 = ListNode (3); p3 = ListNode (4); head. next = p1; p1.next = p2; p2.next = p3; newhead = None; p = recurse (head, newhead ); # output chain table 4-> 3-> 2-> 1-> None while p: print p. val; p = p. next;

The running result is the same as the preceding one.

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