270. Closest Binary Search Tree Value

Problem:

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.

8/19/2018 update:
如果root.val > target, 说明了root的右边肯定离target更远，所以要往左走。
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Analysis:

The result is updated by the smaller different between current node's val and target. 

Solution:

class Solution {
    public int closestValue(TreeNode root, double target) {
        int res = root.val;
        while (root != null) {
            if (Math.abs(root.val - target) < Math.abs(res - target)) {
                res = root.val;
            }
            root = root.val > target ? root.left : root.right;
        }
        return res;
    }
}