<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* doubleIt(ListNode* head) {
        // string s;
        // ListNode* temp=head;
        // while(temp!=NULL)
        // {
        //     s+=char(temp->val+'0');
        //     temp=temp->next;
        // }
        // long long a;
        // a=stoll(s);
        // a=a*2;
        // s=to_string(a);
        // temp = head;
        // for (int i = 0; i < s.length(); i++) 
        // {
        //     temp->val = s[i] - '0';
        //     if (temp->next == NULL && i < s.length() - 1)
        //     {
        //         temp->next = new ListNode(0);
        //     }
        //     temp = temp->next;
        // }
        
        // return head;
        stack<int> s;
        ListNode* temp=head;
        while(temp!=NULL)
        {
            s.push(temp->val);
            temp=temp->next;
        }
        string a;
        int v=0;
        while(!s.empty())
        {
            int x=s.top();
            s.pop();
            if(x>4)
            {
                x=x*2;
                x=x-10+v;
                a+=char(x+'0');
                v=1;
            }
            else
            {
                x=x*2+v;
                a+=char(x+'0');
                v=0;
            }
        }
        string f;
        if(head->val>4)
        {
            f+='1';
        }
        reverse(a.begin(),a.end());
        f+=a;
        cout<<f;
        ListNode* newh;
        temp=head;
        for(int i=0;i<f.length();i++)
        {
            temp->val=f[i]-'0';
            if (temp->next == NULL && i < f.length() - 1) 
            {
                temp->next = new ListNode(0); 
            }
            temp = temp->next;
        }
        
        return head;
    }
};
47775