lec3_1.cpp

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

/**
 * 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) {
        
        vector<int>ans;
        ListNode *temp = head;

        while(temp!=NULL)
        {
            ans.push_back(temp->val);
            temp = temp->next;
        }
        int i = ans.size() -1;
        temp = head;

        while(temp)
        {
            temp->val = ans[i];
            i -- ;
            temp = temp->next;
        }
        return head;
    }
    
};