Convert Sorted Array to Binary Search Tree

Problem

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

Constraints

• 1 <= nums.length <= 104
• -104 <= nums[i] <= 104
• nums is sorted in a strictly increasing order.

Solution

The problem Convert Sorted Array to Binary Search Tree can be solved by setting the middle element as a root node and creating a height-balanced binary search tree on its left and right recursively.

Implementation

/**
 * 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 *sortedArrayRangeToBST(vector<int> &nums, int left, int right)
    {
        if (left > right)
            return NULL;

        int middle = (left + right) / 2;
        TreeNode *root = new TreeNode(nums[middle]);
        root->left = sortedArrayRangeToBST(nums, left, middle - 1);
        root->right = sortedArrayRangeToBST(nums, middle + 1, right);

        return root;
    }
    TreeNode *sortedArrayToBST(vector<int> &nums) { return sortedArrayRangeToBST(nums, 0, nums.size() - 1); }
};