108 将有序数组转换为二叉搜索树

https://leetcode.cn/leetbook/read/top-interview-questions-easy/xninbt/

https://leetcode.cn/problems/convert-sorted-array-to-binary-search-tree/description/

cost: 12m47s

/**
 * 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* sortedArrayToBST(vector<int>& nums) {
        return this->sortedArrayToBST_(nums, 0, nums.size() - 1);
    }

private:
    TreeNode* sortedArrayToBST_(vector<int>& nums, int left, int right) {
        if (left > right) {
            return nullptr;
        }
        if (left == right) {
            return new TreeNode(nums[left]);
        }
        int mid = left + (right - left) / 2;
        auto node = new TreeNode(nums[mid]);
        node->left = this->sortedArrayToBST_(nums, left, mid - 1);
        node->right = this->sortedArrayToBST_(nums, mid + 1, right);
        return node;
    }
};

• 时间复杂度：O(n)
• 空间复杂度：O(n)