*LeetCode-Closest Binary Search Tree Value

啊 最直观的应该是iterative的 每次向下一层 都尝试更新min dist就好 不会因为选择了某一边而错过min dist的！因为假如root 比target大 那root右边那些更大的不可能比root更近！

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

recursive

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