Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.
Example:
Given the sorted array: [-10,-3,0,5,9],
One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
0
/ \
-3 9
/ /
-10 5
Solution:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
TreeNode node = new TreeNode();
return buildTree(nums, 0, nums.length - 1);
}
TreeNode buildTree(int[] nums, int left, int right) {
if (left > right) {
return null;
}
int mid = left + (right - left) / 2;
TreeNode node = new TreeNode(nums[mid]);
node.left = buildTree(nums, left, mid - 1);
node.right = buildTree(nums, mid + 1, right);
return node;
}
}