Convert Sorted Array to Binary Search Tree

Prooblelm

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

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.

Solution

Sorted Vector를 Height balanced로 만들어 준다.

Code

C++

/**
 * 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 sortedArrayToHBT(nums, 0, nums.size());
    }
	//Height Balanced Tree
    TreeNode *sortedArrayToHBT(vector<int> &nums, int start, int end)
    {
        if (end <= start) return NULL;
        int mid = (end + start) / 2;
        TreeNode *root = new TreeNode(nums[mid]);
        root->left = sortedArrayToHBT(nums, start, mid);
        root->right = sortedArrayToHBT(nums, mid + 1, end);
        return root;
    }
};