108.convert-sorted-array-to-binary-search-tree.cpp

/*
 * @lc app=leetcode id=108 lang=cpp
 *
 * [108] Convert Sorted Array to Binary Search Tree
 *
 * https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/
 *
 * algorithms
 * Easy (66.99%)
 * Likes:    7738
 * Dislikes: 393
 * Total Accepted:    830.3K
 * Total Submissions: 1.2M
 * Testcase Example:  '[-10,-3,0,5,9]'
 *
 * Given an integer array nums where the elements are sorted in ascending
 * order, convert it to a height-balanced binary search tree.
 *
 * A height-balanced binary tree is a binary tree in which the depth of the two
 * subtrees of every node never differs by more than one.
 *
 *
 * Example 1:
 *
 *
 * Input: nums = [-10,-3,0,5,9]
 * Output: [0,-3,9,-10,null,5]
 * Explanation: [0,-10,5,null,-3,null,9] is also accepted:
 *
 *
 *
 * Example 2:
 *
 *
 * Input: nums = [1,3]
 * Output: [3,1]
 * Explanation: [1,null,3] and [3,1] are both height-balanced BSTs.
 *
 *
 *
 * Constraints:
 *
 *
 * 1 <= nums.length <= 10^4
 * -10^4 <= nums[i] <= 10^4
 * nums is sorted in a strictly increasing order.
 *
 *
 */

// @lc code=start
/**
 * 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 *A(vector<int> &nums, int l, int r)
    {
        if (l > r)
            return NULL;
        int mid = (r + l) / 2;
        TreeNode *root = new TreeNode(nums[mid], A(nums, l, mid - 1), A(nums, mid + 1, r));
        return root;
    }
    TreeNode *sortedArrayToBST(vector<int> &nums)
    {
        return A(nums, 0, nums.size() - 1);
    }
};
// @lc code=end