108. Convert Sorted Array to Binary Search Tree
Time: O(n), Space: O(n)
/**
* 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 || nums.length == 0) {
return null;
}
return sortedArrayToBST(nums, 0, nums.length - 1);
}
private TreeNode sortedArrayToBST(int[] nums, int start, int end) {
if (start > end) {
return null;
}
int mid = (start + end) / 2;
TreeNode node = new TreeNode(nums[mid]);
node.left = sortedArrayToBST(nums, start, mid - 1);
node.right = sortedArrayToBST(nums, mid + 1, end);
return node;
}
}