270. 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.

Solution 1. Iteration
/**
 * 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) {
        double diff = Double.MAX_VALUE;
        int val = root.val;
        
        while (root != null) {
            if (diff > Math.abs(root.val - target)) {
                val = root.val;
                diff = Math.abs(root.val - target);
            }
            if (root.val > target) {
                root = root.left;
            } else {
                root = root.right;
            }
        } 
        
        return val;
    }
}

Solution 2. Recursion
public class Solution {
    public int closestValue(TreeNode root, double target) {
        int a = root.val;
        TreeNode kid = target < a ? root.left : root.right;
        if (kid == null) return a;
        int b = closestValue(kid, target);
        return Math.abs(a - target) < Math.abs(b - target) ? a : b;
    }    
}