<p>You are given the <code>head</code> of a <strong>non-empty</strong> linked list representing a non-negative integer without leading zeroes.</p>

<p>Return <em>the </em><code>head</code><em> of the linked list after <strong>doubling</strong> it</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2023/05/28/example.png" style="width: 401px; height: 81px;" />
<pre>
<strong>Input:</strong> head = [1,8,9]
<strong>Output:</strong> [3,7,8]
<strong>Explanation:</strong> The figure above corresponds to the given linked list which represents the number 189. Hence, the returned linked list represents the number 189 * 2 = 378.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2023/05/28/example2.png" style="width: 401px; height: 81px;" />
<pre>
<strong>Input:</strong> head = [9,9,9]
<strong>Output:</strong> [1,9,9,8]
<strong>Explanation:</strong> The figure above corresponds to the given linked list which represents the number 999. Hence, the returned linked list reprersents the number 999 * 2 = 1998. 
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the list is in the range <code>[1, 10<sup>4</sup>]</code></li>
	<li><font face="monospace"><code>0 &lt;= Node.val &lt;= 9</code></font></li>
	<li>The input is generated such that the list represents a number that does not have leading zeros, except the number <code>0</code> itself.</li>
</ul>

/**
 * 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* reverse(ListNode* head){
        if(head->next == nullptr) return head;
        ListNode* nxt = head->next;
        ListNode* prev = head;
        prev->next = nullptr;
        while(nxt!=nullptr){
            ListNode* tt = nxt->next;
            nxt->next = prev;
            prev = nxt;
            nxt = tt;
        }
        return prev;
    }
    ListNode* doubleIt(ListNode* head) {
        ListNode* temp = head;
        vector<int> s;
        unsigned long long x = 0;
        while(temp!=nullptr){
            s.push_back(temp->val);
            temp = temp->next;
        }
        temp = head;
        ListNode* prev = head;
        int n = s.size();
        int c = 0;
        for(int i = n-1 ; i>=0 ; i--){
            s[i]*=2;
            if(c==1){
                s[i]++;
                c=0;
            }
            if(s[i]>=10){
                s[i]%=10;
                c=1;
            }
            temp->val = s[i];
            prev = temp;
            temp = temp->next;
        }
        if(c==1){
            ListNode* t = new ListNode(1);
            prev->next = t;
        }
        
        return reverse(head);
       
    }
};
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