206. Reverse Linked List (List)

/**
 * 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) {
        if(!head) return head;
        
        ListNode* preHead = head;
        ListNode* current = preHead->next;
        ListNode* curNext;
        head->next = NULL;
        
        while(current){
            curNext = current->next;
            current->next = preHead;
            preHead = current;
            current = curNext;
        }
        return preHead;
    }
};