fix few details, binary search trees

src/trees/binary_tree.py

@@ -0,0 +1,173 @@
+#!/usr/bin/python
+
+__author__ = "Mari Wahl"
+__email__ = "marina.w4hl@gmail.com"
+
+
+
+''' Implementation of a binary tree and its properties. For example, the following bt:
+
+                               1                ---> level 0
+                        2             3         ---> level 1
+                  4         5                   ---> level 2
+              6      7                          ---> level 3
+            8   9                               ---> level 4
+
+    has the following properties:
+
+        - SIZE OR NUMBER OF NODES: n = 9
+        - NUMBER OF BRANCHES OR INTERNAL NODES: b = n-1 = 8
+        - VALUE OF ROOT = 1
+        - MAX_DEPTH OR HEIGHT: h = 4
+        - IS BALANCED? NO
+        - IS BST? NO
+'''
+
+
+class NodeBT(object):
+    def __init__(self, item=None, level=0):
+        self.item = item
+        self.level = level
+        self.left = None
+        self.right = None
+
+
+    def __repr__(self):
+        return '{}'.format(self.item)
+
+
+    def _addNextNode(self, value, level_here=1):
+        new_node = NodeBT(value, level_here)
+        if not self.item:
+            self.item = new_node
+        elif not self.left:
+            self.left = new_node
+        elif not self.right:
+            self.right = new_node
+        else:
+            self.left = self.left._addNextNode(value, level_here+1)
+        return self
+
+
+    def _searchForNode(self, value):
+        if self.item == value:
+            return self
+        else:
+            found = None
+            if self.left:
+                found = self.left._searchForNode(value)
+            if self.right:
+                found =  found or self.right._searchForNode(value)
+            return found
+
+
+    def _isLeaf(self):
+        return not self.right and not self.left
+
+
+    def _getMaxHeight(self):
+        ''' Get the max height at the node, O(n)'''
+        levelr, levell = 0, 0
+        if self.right:
+            levelr = self.right._getMaxHeight() + 1
+        if self.left:
+            levell = self.left._getMaxHeight() + 1
+        return max(levelr, levell)
+
+
+    def _getMinHeight(self, level=0):
+        ''' Get the min height at the node, O(n)'''
+        levelr, levell = -1, -1
+        if self.right:
+            levelr = self.right._getMinHeight(level +1)
+        if self.left:
+            levell = self.left._getMinHeight(level +1)
+        return min(levelr, levell) + 1
+
+
+    def _isBalanced(self):
+        ''' Find whether the tree is balanced, by calculating heights first, O(n2) '''
+        if self._getMaxHeight() - self._getMinHeight() < 2:
+            return False
+        else:
+            if self._isLeaf():
+                return True
+            elif self.left and self.right:
+                return self.left._isBalanced() and   self.right._isBalanced()
+            elif not self.left and self.right:
+                return  self.right._isBalanced()
+            elif not self.right and self.left:
+                 return  self.left._isBalanced()
+
+    def _isBST(self):
+        ''' Find whether the tree is a BST, inorder '''
+        if self.item:
+            if self._isLeaf():
+                return True
+            elif self.left:
+                if self.left.item < self.item:
+                    return self.left._isBST()
+                else:
+                    return False
+            elif self.right:
+                if self.right.item > self.item:
+                    return self.right._isBST()
+                else:
+                    return False
+        else:
+            raise Exception('Tree is empty')
+
+
+
+
+
+class BinaryTree(object):
+
+    def __init__(self):
+        self.root = None
+
+
+    def addNode(self, value):
+        if not self.root:
+            self.root = NodeBT(value)
+        else:
+            self.root._addNextNode(value)
+
+
+    def isLeaf(self, value):
+        node = self.root._searchForNode(value)
+        return node._isLeaf()
+
+    def getNodeLevel(self, item):
+        node = self.root._searchForNode(item)
+        if node:
+            return node.level
+        else:
+            raise Exception('Node not found')
+
+    def isRoot(self, value):
+        return self.root.item == value
+
+    def getHeight(self):
+        return self.root._getMaxHeight()
+
+    def isBalanced(self):
+        return self.root._isBalanced()
+
+    def isBST(self):
+        return self.root._isBST()
+
+
+
+if __name__ == '__main__':
+    bt = BinaryTree()
+    print "Adding nodes 1 to 10 in the tree..."
+    for i in range(1, 10):
+        bt.addNode(i)
+    print "Is 8 a leaf? ", bt.isLeaf(8)
+    print "Whats the level of node 8? ", bt.getNodeLevel(8)
+    print "Is node 10 a root? ", bt.isRoot(10)
+    print "Is node 1 a root? ", bt.isRoot(1)
+    print "Whats the tree height? ", bt.getHeight()
+    print "Is this tree BST? ", bt.isBST()
+    print "Is this tree balanced? ", bt.isBalanced()