Convert Sorted List to Binary Search Tree

단일 링크드 리스트의 헤드 노드 포인터를 받고,

이 리스트를 트리의 좌우 높이가 같은 바이너리 트리로 변환하는 문제

/**
 * 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 == nullptr)
        {
            return nullptr;
        }

        static vector<ListNode*> nodes(MaximumItem);
        
        ListNode* temp{head};
        int index{0};
        while (temp != nullptr)
        {
            nodes[index] = temp;
            temp = temp->next;
            ++index;
        }

        return DivideAndConquer(0, index - 1, nodes);
    }
private:
    const int MaximumItem = 20000;

    TreeNode* DivideAndConquer(int start, int end, vector<ListNode*>& nodes)
    {
        if (start == end)
        {
            return new TreeNode(nodes[start]->val);
        }

        TreeNode* tree{nullptr};
        if (1 < end - start)
        {
            int middle{((end - start) >> 1) + start};
            tree = new TreeNode(nodes[middle]->val);
            tree->left = DivideAndConquer(start, middle - 1, nodes);
            tree->right = DivideAndConquer(middle + 1, end, nodes);
        }
        else
        {
            tree = new TreeNode(nodes[end]->val);
            tree->left = DivideAndConquer(start, end - 1, nodes);
        }
        
        return tree;
    }
};