reverse-linked-list.cpp

// Reverse a singly linked list.
//
// Example:
//
//
// Input: 1->2->3->4->5->NULL
// Output: 5->4->3->2->1->NULL
//
//
// Follow up:
//
// A linked list can be reversed either iteratively or recursively. Could you implement both?
//


/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *newHead = new ListNode(-1);
        ListNode *p = head;
        while (p) {
            ListNode *n = newHead->next;
            newHead->next = p;
            p = p->next;
            newHead->next->next = n;
        }
        p = newHead->next;
        delete newHead;
        return p;
    }
};