main.cpp

/**
 * 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* sortedListToBST(ListNode* head) {
        if (!head) return nullptr;

        ListNode dummy(0, head);
        ListNode *fast = &dummy, *slow = &dummy;
        while (fast->next && fast->next->next) {
            slow = slow->next;
            fast = fast->next->next;
        }

        auto root = new TreeNode(slow->next->val);

        root->right = sortedListToBST(slow->next->next);

        slow->next = nullptr;
        if (slow != &dummy) root->left = sortedListToBST(head);

        return root;
    }
};