Convert Sorted Array to Binary Search Tree

Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

» Solve this problem

Complexity: O(n)

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode *sortedArrayToBST(vector &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return toBST(num, 0, num.size() - 1);
    }
    
    TreeNode *toBST(vector &num, int start, int end) {
        if (end < start) {
            return NULL;
        }
        
        int mid = (start + end) / 2;
        TreeNode *root = new TreeNode(num[mid]);
        root->left = toBST(num, start, mid - 1);
        root->right = toBST(num, mid + 1, end);
        return root;
    }
};