# BST Closest Nodeby Isai Damier, Android Engineer @ Google

```  #=====================================================================
# Author: Isai Damier
# Title: Closest Node
# Project: geekviewpoint
# Package: algorithms
#
# Statement:
#   Retrieve the node whose value is closest to the given value.
#
# Time Complexity of Solution:
#   Best = const; Average = O(log(n)); Worst = O(n).
#
# Technical Details: From a logic viewpoint, if the given element is
#   on the tree, then it is closest to itself. Furthermore, At any
#   given time, a value falls between two other values, such as
#   x <= el <= y, where el falls between x and y. Therefore, as el is
#   searched through the tree, there only needs to track two values:
#   low and high. In the end, whichever of low and high is closer to
#   el is returned; i.e. the wrapping node is return. (In case of a
#   tie, high is returned.)
#
#=====================================================================

class BST( object ):

def __init__( self ):
self.root = None

def getRoot( self ):
return self.root

def closestNode( self, el ):
if self.root is None:
return None

n = self.root
high, low = None, None
while n != None and el != n.data:
if el < n.data:
high = n
n = n.left
else:
low = n
n = n.right

if n is not None:
return n

if None != high and None != low:
return low if ( high.data - el ) > ( el - low.data ) else high

if None != high:
return high

return low;
```
```import unittest
from algorithms.BST import BST
from cStringIO import StringIO
import sys
class Test( unittest.TestCase ):
#=====================================================================
# Test of closestmethod, of class BST.
#=====================================================================
def testClosestNode( self ):
bst = BST()

self.assertIsNone( bst.closestNode( 275 ) )
treeTape = [200, 100, 300, 50, 150, 250, 350, 25, 75, 125,
175, 225, 275, 325, 375, 35, 212, 312, 400]
for i in treeTape:

# load data into tree
for i in treeTape:

self.assertEquals( len( treeTape ), bst.size() ) # has correct size

# test closestNode
self.assertEquals( 200, bst.closestNode( 200 ).data )
self.assertEquals( 400, bst.closestNode( 500 ).data )
self.assertEquals( 25, bst.closestNode( 1 ).data )
self.assertEquals( 175, bst.closestNode( 180 ).data )
self.assertEquals( 200, bst.closestNode( 190 ).data )
self.assertEquals( 350, bst.closestNode( 356 ).data )
self.assertEquals( 35, bst.closestNode( 30 ).data )
self.assertEquals( 225, bst.closestNode( 219 ).data )
self.assertEquals( 212, bst.closestNode( 218 ).data )
self.assertEquals( 150, bst.closestNode( 150 ).data )

self.assertEquals( len( treeTape ), bst.size() ) # has correct size
```