Added implementation for Splay Trees.

Added code for splay trees with public APIs insert, delete, splay. The work is in reference with issue codezonediitj#109

pydatastructs/trees/__init__.py

@@ -6,7 +6,7 @@
 )
 
 from .binary_trees import (
-    TreeNode, BinaryTree, BinarySearchTree, BinaryTreeTraversal, AVLTree
+    TreeNode, BinaryTree, BinarySearchTree, BinaryTreeTraversal, AVLTree, SplayTree
 )
 __all__.extend(binary_trees.__all__)
 

pydatastructs/trees/binary_trees.py

@@ -10,7 +10,8 @@
     'AVLTree',
     'BinaryTree',
     'BinarySearchTree',
-    'BinaryTreeTraversal'
+    'BinaryTreeTraversal',
+    'SplayTree'
 ]
 
 class BinaryTree(object):
@@ -783,3 +784,67 @@ def breadth_first_search(self, node=None, strategy='queue'):
             if tree[node].right is not None:
                 q.append(tree[node].right)
         return visit
+
+
+class SplayTree(AVLTree):
+        """
+        Represents Splay Trees.
+        References
+        ==========
+        [1] https://en.wikipedia.org/wiki/Splay_tree
+
+        """
+        def _zig(self,x,p):
+                if(self.tree[p].left==x):
+                        super(SplayTree,self)._right_rotate(p,x)
+                else:
+                        super(SplayTree,self)._left_rotate(p,x)
+
+        def _zig_zig(self,x,p):
+                super(SplayTree,self)._right_rotate(self.tree[p].parent,p)
+                super(SplayTree,self)._right_rotate(p,x)
+
+        def _zig_zag(self,x,p):
+                super(SplayTree,self)._left_rotate(p,x)
+                super(SplayTree,self)._right_rotate(self.tree[x].parent,x)
+
+        def _zag_zag(self,x,p):
+                super(SplayTree,self)._left_rotate(self.tree[p].parent,p)
+                super(SplayTree,self)._left_rotate(p,x)
+
+        def _zag_zig(self,x,p):
+                super(SplayTree,self)._right_rotate(p,x)
+                super(SplayTree,self)._left_rotate(self.tree[x].parent,x)
+
+        def splay(self,x,p):
+                while self.tree[x].parent is not None:
+                        if(self.tree[p].parent is None):
+                                self._zig(x,p)
+                        elif(self.tree[p].left==x and self.tree[self.tree[p].parent].left == p):
+                                self._zig_zig(x,p)
+                        elif(self.tree[p].right==x and self.tree[self.tree[p].parent].right == p):
+                                self._zag_zag(x,p)
+                        elif(self.tree[p].left==x and self.tree[self.tree[p].parent].right == p):
+                                self._zag_zig(x,p)
+                        else:
+                                self._zig_zag(x,p)
+                        p = self.tree[x].parent
+
+
+        def insert(self,key,x):
+                super(AVLTree, self).insert(key, x)
+                e, p = super(AVLTree,self).search(x,parent=True)
+                self.tree[self.size-1].parent = p;
+                self.splay(e, p)
+
+        def delete(self,x):
+                b = super(AVLTree,self).delete(x,balancing_info=True)
+                self.splay(b,self.tree[b].parent)
+                return True
+
+        def join(self,tree2):
+                raise NotImplementedError("This is not implemented yet.")
+
+
+        def split(self,x):
+                raise NotImplementedError("This is not implemented yet.")