Leetcode: Closest Binary Search Tree Value

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.

Note:

• Given target value is a floating point.
• You are guaranteed to have only one unique value in the BST that is closest to the target.

Code (Java):

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private double min = Double.MAX_VALUE;
    private int ans = 0;
    public int closestValue(TreeNode root, double target) {
        if (root == null) {
            return Integer.MAX_VALUE;
        }
        
        closestValueHelper(root, target);
        
        return ans;
    }
    
    private void closestValueHelper(TreeNode root, double target) {
        if (root == null) {
            return;
        }
        
        if (Math.abs((double) root.val - target) < min) {
            min = Math.abs((double) root.val - target);
            ans = root.val;
        }
        
        if (root.val > target) {
            closestValueHelper(root.left, target);
        } else if (root.val < target) {
            closestValueHelper(root.right, target);
        }
    }
}

Iterative solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int closestValue(TreeNode root, double target) {
        if (root == null) {
            throw new NullPointerException("Tree must be non-empty");
        }
        
        int result = 0;
        double gap = Double.MAX_VALUE;
        
        while (root != null) {
            if (root.val == target) {
                return root.val;
            }
            
            double dist = Math.abs(root.val - target);
            if (dist < gap) {
                result = root.val;
                gap = dist;
            }
            
            if (target > root.val) {
                root = root.right;
            } else if (target < root.val) {
                root = root.left;
            }
        }
        return result;
    }
}