<p>Given the <code>head</code> of a singly linked list where elements are sorted in <strong>ascending order</strong>, convert <em>it to a </em><span data-keyword="height-balanced"><strong><em>height-balanced</em></strong></span> <em>binary search tree</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/08/17/linked.jpg" style="width: 500px; height: 388px;" />
<pre>
<strong>Input:</strong> head = [-10,-3,0,5,9]
<strong>Output:</strong> [0,-3,9,-10,null,5]
<strong>Explanation:</strong> One possible answer is [0,-3,9,-10,null,5], which represents the shown height balanced BST.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> head = []
<strong>Output:</strong> []
</pre>

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

<ul>
	<li>The number of nodes in <code>head</code> is in the range <code>[0, 2 * 10<sup>4</sup>]</code>.</li>
	<li><code>-10<sup>5</sup> &lt;= Node.val &lt;= 10<sup>5</sup></code></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) {}
 * };
 */
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    public:
    TreeNode* helper(vector<int>&vec,int i,int j){
        if(i>j) return NULL;
        int mid=(i+j)/2;
        TreeNode* root=new TreeNode(vec[mid]);
        root->left=helper(vec,i,mid-1);
        root->right=helper(vec,mid+1,j);

        return root;
    }

    TreeNode* sortedListToBST(ListNode* head) {
        vector<int>result;
        ListNode* temp=head;
        while(temp!=NULL){
            result.push_back(temp->val);
            temp=temp->next;
        }
        int i=0,j=result.size()-1;
      return  helper(result,i,j);
     /*   if(head==NULL) return NULL;
        if(head->next==NULL) return new TreeNode(head->val);
        ListNode* slow=head;
        ListNode* fast=head;
        ListNode* prev=NULL;
        while(fast!=NULL&&fast->next!=NULL){
            prev=slow;
            slow=slow->next;
            fast=fast->next->next;
        }
        TreeNode* root=new TreeNode(slow->val);
        prev->next=NULL;
        root->left=sortedListToBST(head);
        root->right=sortedListToBST(slow->next);


        return root;*/
    }
};
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