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   3Output: 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;    }}