270. Closest Binary Search Tree Value

题目：

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.

链接： http://leetcode.com/problems/closest-binary-search-tree-value/

3/5/2017

出现的问题：

1. 这道题绝对不是把minH, maxL设为Integer最大最小值就可以了。因为有可能target就是很接近这两个值的double值，得出错的结果。

2. 当minH, maxL有一个为null的时候，返回另外一个值。都不为null时再比较绝对值。

public class Solution {
    public int closestValue(TreeNode root, double target) {
        Integer minH = null;
        Integer maxL = null;
        
        while (root != null) {
            if (root.val > target) {
                if (minH == null || root.val < minH) minH = root.val;
                root = root.left;
            } else {
                if (maxL == null || root.val > maxL) maxL = root.val;
                root = root.right;
            }
        }
        if (minH == null) return maxL;
        else if (maxL == null) return minH;
        return target - maxL < minH - target? maxL: minH;
    }
}

别人的做法更好，只需要一个minDiff就可以了，并且minDiff可以初始化为root.val，简化非常多。