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.

/**
 * 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 abs = Math.abs(target-root.val);
        int res = 0;
        while(root != null){
            if(abs>= Math.abs(target-root.val)){
                res = root.val;
                abs = Math.abs(target-root.val);
            }
            if(target<root.val) root = root.left;
            else root = root.right;
        }
        return res;
    }
}