206. Reverse Linked List

反转链表

注意是借用  假的头节点,这样算法判断开始和结束,就好很多了.

借用头插法.

[]dummy/head

[]　　[]　　 []　　 []

head  curr

====

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode dummy(-1);//假的头节点
        ListNode *curr = head;

        head = &dummy;
        while(curr)
        {
            ListNode *tmp = curr->next;
            curr->next = head->next;
            head->next = curr;
            curr = tmp;
        }

        return dummy.next;
    }
};