270. Closest Binary Search Tree Value

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

/*
Iterative Solution

Time Complexity: O(N) - If the tree is skewed it will visit all nodes.
Space Complexity: O(1)
N = Total number of nodes in the BST
*/
class Solution {
    public int closestValue(TreeNode root, double target) throws NullPointerException {
        if (root == null) {
            throw new NullPointerException("Input Tree root is null");
        }

        int closest = root.val;
        while (root != null) {
            if (Math.abs(root.val - target) < Math.abs(closest - target)) {
                closest = root.val;
            }
            if (target == root.val) {
                break;
            }
            root = target < root.val ? root.left : root.right;
        }

        return closest;
    }
}


/*
Recursive Solution

Time Complexity: O(N) - If the tree is skewed it will visit all nodes.
Space Complexity: O(H)
N = Total number of nodes in the BST
H = Height of the binary Tree. (Recursion Stack)
*/
class Solution {
    public int closestValue(TreeNode root, double target) throws NullPointerException {
        if (root == null) {
            throw new NullPointerException("Input Tree root is null");
        }

        int[] closest = new int[1];
        closest[0] = root.val;
        closestValueHelper(closest, root, target);
        return closest[0];
    }

    public void closestValueHelper(int[] closest, TreeNode node, double target) {
        if (node == null) {
            return;
        }
        if (target == node.val) {
            closest[0] = node.val;
            return;
        }
        if (Math.abs(node.val - target) < Math.abs(closest[0] - target)) {
                closest[0] = node.val;
        }
        if (target < node.val) {
            closestValueHelper(closest, node.left, target);
        } else {
            closestValueHelper(closest, node.right, target);
        }
    }
}