【python算法】单链表的反转

1.循环反转单链表

循环的方法中，使用pre指向前一个结点，cur指向当前结点，每次把cur->next指向pre即可

#coding="utf-8"

class ListNode:
    def __init__(self, x):
        self.val = x;
        self.next = None;

def nonrecurse(head):
    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);
p1 = ListNode(2);
p2 = ListNode(3);
p3 = ListNode(4);
head.next = p1;
p1.next = p2;
p2.next = p3;
p = nonrecurse(head);
while p:
    print p.val;
    p = p.next;