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/**
 * 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:
    ListNode* ghead;
    int getSize(ListNode *head){
        int sz = 0;
        while(head){
            sz++;
            head = head->next;
        }
        return sz;
    }

    TreeNode* convertListToBST(int l, int r){
        if(l > r) return NULL;

        int mid = (l+r)>>1;
        // Left node.
        TreeNode *left = convertListToBST(l, mid-1);

        // Middle node.
        TreeNode *node = new TreeNode(ghead->val);
        ghead = ghead->next;

        //Right node.
        TreeNode *right = convertListToBST(mid+1, r);

        //Assign left, right and return node.
        node->left = left;
        node->right = right;
        return node;
    }

    TreeNode* sortedListToBST(ListNode* head) {
        int sz = getSize(head);
        ghead = head;
        return convertListToBST(0, sz-1);
    }
};