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.

Example:

Input: root = [4,2,5,1,3], target = 3.714286

    4
   / 
  2   5
 / 
1   3

Output: 4

binary search

time: O(h), space: O(1)　　-- h: height of the tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int closestValue(TreeNode root, double target) {
        TreeNode node = root;
        int min = root.val;
        while(node != null) {
            if(Math.abs(node.val - target) < Math.abs(min - target)) {
                min = node.val;
            }
            node = node.val > target ? node.left : node.right;
        }
        return min;
    }
}