reverse_linked_list.cpp

// https://leetcode.com/problems/reverse-linked-list/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode *prevNode, *nextNode, *currNode;
        
        if (head == NULL) return head;
        
        ListNode *trueHead = head;
        prevNode = head;
        currNode = head->next;
        
        while(currNode != NULL) {
            nextNode = currNode->next;
            currNode->next = prevNode;
            prevNode = currNode;
            currNode = nextNode;
        }
        trueHead->next = NULL;
        
        return prevNode;
    }
};