108

108. Convert Sorted Array to Binary Search Tree (Easy)

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: [1,3] and [3,1] are both a height-balanced BSTs.

 

Constraints:

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

Companies:
Amazon, Facebook, Google, Apple

Related Topics:
Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree

Similar Questions:

• Convert Sorted List to Binary Search Tree (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(logN)
class Solution {
    TreeNode *dfs(vector<int> &A, int begin, int end) {
        if (begin + 1 > end) return NULL;
        int mid = (begin + end) / 2;
        auto root = new TreeNode(A[mid]);
        root->left = dfs(A, begin, mid);
        root->right = dfs(A, mid + 1, end);
        return root;
    }
public:
    TreeNode* sortedArrayToBST(vector<int>& A) {
        return dfs(A, 0, A.size());
    }
};