Description
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:
tree
Solution
DFS, time O(n), space O(h)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
if (nums == null) {
return null;
}
return dfs(nums, 0, nums.length);
}
public TreeNode dfs(int[] nums, int s, int e) {
if (s >= e) {
return null;
}
int m = s + (e - s) / 2;
TreeNode root = new TreeNode(nums[m]);
root.left = dfs(nums, s, m);
root.right = dfs(nums, m + 1, e);
return root;
}
}
