[WIP] Added binary tree traversals (#21)

* Added BinaryTreeTraversal

* `peek` and `is_converge` added to stack

.gitignore

@@ -6,3 +6,6 @@ __pycache__/
 .pytest_cache/
 pre_commit.ps1
 .coverage
+htmlcov
+# for developement purposes
+pds_debug.py

pydatastructs/miscellaneous_data_structures/stack.py

@@ -60,7 +60,7 @@ def __new__(cls, implementation='array', **kwargs):
         if implementation == 'array':
             return ArrayStack(
                 kwargs.get('maxsize', None),
-                kwargs.get('top', None),
+                kwargs.get('top', 0),
                 kwargs.get('items', None),
                 kwargs.get('dtype', int))
         raise NotImplementedError(
@@ -74,6 +74,14 @@ def pop(self, *args, **kwargs):
         raise NotImplementedError(
               "This is an abstract method.")
 
+    @property
+    def is_empty(self):
+        return None
+
+    @property
+    def peek(self):
+        return None
+
 class ArrayStack(Stack):
 
     def __new__(cls, maxsize=None, top=0, items=None, dtype=int):
@@ -107,6 +115,14 @@ def pop(self):
         self.items[self.top] = None
         return r
 
+    @property
+    def is_empty(self):
+        return self.top == 0
+
+    @property
+    def peek(self):
+        return self.items[self.top - 1]
+
     def __str__(self):
         """
         Used for printing.

pydatastructs/trees/__init__.py

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

pydatastructs/trees/binary_trees.py

@@ -1,10 +1,15 @@
 from __future__ import print_function, division
 from pydatastructs.utils import Node
+from pydatastructs.miscellaneous_data_structures import Stack
+from pydatastructs.linear_data_structures import OneDimensionalArray
+# TODO: REPLACE COLLECTIONS QUEUE WITH PYDATASTRUCTS QUEUE
+from collections import deque as Queue
 
 __all__ = [
     'Node',
     'BinaryTree',
-    'BinarySearchTree'
+    'BinarySearchTree',
+    'BinaryTreeTraversal'
 ]
 
 class BinaryTree(object):
@@ -243,3 +248,194 @@ def delete(self, key):
                     self.tree[parent].right = child
 
         return True
+
+class BinaryTreeTraversal(object):
+    """
+    Represents the traversals possible in
+    a binary tree.
+
+    Parameters
+    ==========
+
+    tree: BinaryTree
+        The binary tree for whose traversal
+        is to be done.
+
+    Traversals
+    ==========
+
+    - Depth First Search
+        In Order, Post Order, Pre Order Out Order
+
+    - Breadth First Search
+
+    Examples
+    ========
+
+    >>> from pydatastructs import BinarySearchTree as BST
+    >>> from pydatastructs import BinaryTreeTraversal as BTT
+    >>> b = BST(2, 2)
+    >>> b.insert(1, 1)
+    >>> b.insert(3, 3)
+    >>> trav = BTT(b)
+    >>> dfs = trav.depth_first_search()
+    >>> [str(n) for n in dfs]
+    ['(None, 1, 1, None)', '(1, 2, 2, 2)', '(None, 3, 3, None)']
+    >>> bfs = trav.breadth_first_search()
+    >>> [str(n) for n in bfs]
+    ['(1, 2, 2, 2)', '(None, 1, 1, None)', '(None, 3, 3, None)']
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Tree_traversal
+    """
+
+    __slots__ = ['tree']
+
+    def __new__(cls, tree):
+        if not isinstance(tree, BinaryTree):
+            raise TypeError("%s is not a binary tree"%(tree))
+        obj = object.__new__(cls)
+        obj.tree = tree
+        return obj
+
+    def _pre_order(self, node):
+        """
+        Utility method for computing pre-order
+        of a binary tree using iterative algorithm.
+        """
+        visit = []
+        if node == None:
+            return visit
+        tree, size = self.tree.tree, self.tree.size
+        s = Stack(maxsize=size)
+        s.push(node)
+        while not s.is_empty:
+            node = s.pop()
+            visit.append(tree[node])
+            if tree[node].right != None:
+                s.push(tree[node].right)
+            if tree[node].left != None:
+                s.push(tree[node].left)
+        return visit
+
+    def _in_order(self, node):
+        """
+        Utility method for computing in-order
+        of a binary tree using iterative algorithm.
+        """
+        visit = []
+        tree, size = self.tree.tree, self.tree.size
+        s = Stack(maxsize=size)
+        while not s.is_empty or node != None:
+            if node != None:
+                s.push(node)
+                node = tree[node].left
+            else:
+                node = s.pop()
+                visit.append(tree[node])
+                node = tree[node].right
+        return visit
+
+    def _post_order(self, node):
+        """
+        Utility method for computing post-order
+        of a binary tree using iterative algorithm.
+        """
+        visit = []
+        tree, size = self.tree.tree, self.tree.size
+        s = Stack(maxsize=size)
+        s.push(node)
+        last = OneDimensionalArray(int, size)
+        last.fill(False)
+        while not s.is_empty:
+            node = s.peek
+            l, r = tree[node].left, tree[node].right
+            cl, cr = l == None or last[l], r == None or last[r]
+            if cl and cr:
+                s.pop()
+                visit.append(tree[node])
+                last[node] = True
+                continue
+            if not cr:
+                s.push(r)
+            if not cl:
+                s.push(l)
+        return visit
+
+    def _out_order(self, node):
+        """
+        Utility method for computing out-order
+        of a binary tree using iterative algorithm.
+        """
+        return reversed(self._in_order(node))
+
+    def depth_first_search(self, order='in_order', node=None):
+        """
+        Computes the depth first search traversal of the binary
+        trees.
+
+        Parameters
+        ==========
+
+        order : str
+            One of the strings, 'in_order', 'post_order',
+            'pre_order', 'out_order'.
+            By default, it is set to, 'in_order'.
+        node : int
+            The index of the node from where the traversal
+            is to be instantiated.
+
+        Returns
+        =======
+
+        list
+            Each element is of type 'Node'.
+        """
+        if node == None:
+            node = self.tree.root_idx
+        if order not in ('in_order', 'post_order', 'pre_order', 'out_order'):
+            raise NotImplementedError(
+                "%s order is not implemented yet."
+                "We only support `in_order`, `post_order`, "
+                "`pre_order` and `out_order` traversals.")
+        return getattr(self, '_' + order)(node)
+
+    def breadth_first_search(self, node=None, strategy='queue'):
+        # TODO: IMPLEMENT ITERATIVE DEEPENING-DEPTH FIRST SEARCH STRATEGY
+        """
+        Computes the breadth first search traversal of a binary tree.
+
+        Parameters
+        ==========
+
+        strategy : str
+            The strategy using which the computation has to happen.
+            By default, it is set 'queue'.
+        node : int
+            The index of the node from where the traversal has to be instantiated.
+            By default, set to, root index.
+
+        Returns
+        =======
+
+        list
+            Each element of the list is of type `Node`.
+        """
+        strategies = ('queue',)
+        if strategy not in strategies:
+            raise NotImplementedError(
+                "%s startegy is not implemented yet"%(strategy))
+        if node == None:
+            node = self.tree.root_idx
+        q, visit, tree = Queue(), [], self.tree.tree
+        q.append(node)
+        while len(q) > 0:
+            node = q.popleft()
+            visit.append(tree[node])
+            if tree[node].left != None:
+                q.append(tree[node].left)
+            if tree[node].right != None:
+                q.append(tree[node].right)
+        return visit

pydatastructs/trees/space_partitioning_trees.py

@@ -1,4 +1,5 @@
 from pydatastructs.utils import Node
+# TODO: REPLACE COLLECTIONS QUEUE WITH PYDATASTRUCTS QUEUE
 from collections import deque as Queue
 from pydatastructs.linear_data_structures.arrays import _check_type
 

pydatastructs/trees/tests/test_binary_trees.py

@@ -1,4 +1,5 @@
-from pydatastructs.trees.binary_trees import BinarySearchTree
+from pydatastructs.trees.binary_trees import (
+    BinarySearchTree, BinaryTreeTraversal)
 from pydatastructs.utils.raises_util import raises
 
 def test_BinarySearchTree():
@@ -32,3 +33,46 @@ def test_BinarySearchTree():
     bc = BST(1, 1)
     assert bc.insert(1, 2) == None
     raises(ValueError, lambda: BST(root_data=6))
+
+def test_BinaryTreeTraversal():
+    BST = BinarySearchTree
+    BTT = BinaryTreeTraversal
+    b = BST('F', 'F')
+    b.insert('B', 'B')
+    b.insert('A', 'A')
+    b.insert('G', 'G')
+    b.insert('D', 'D')
+    b.insert('C', 'C')
+    b.insert('E', 'E')
+    b.insert('I', 'I')
+    b.insert('H', 'H')
+    trav = BTT(b)
+    pre = trav.depth_first_search(order='pre_order')
+    assert [str(n) for n in pre] == \
+    ["(1, 'F', 'F', 3)", "(2, 'B', 'B', 4)", "(None, 'A', 'A', None)",
+     "(5, 'D', 'D', 6)", "(None, 'C', 'C', None)", "(None, 'E', 'E', None)",
+     "(None, 'G', 'G', 7)", "(8, 'I', 'I', None)", "(None, 'H', 'H', None)"]
+    ino = trav.depth_first_search()
+    assert [str(n) for n in ino] == \
+    ["(None, 'A', 'A', None)", "(2, 'B', 'B', 4)", "(None, 'C', 'C', None)",
+     "(5, 'D', 'D', 6)", "(None, 'E', 'E', None)", "(1, 'F', 'F', 3)",
+     "(None, 'G', 'G', 7)", "(None, 'H', 'H', None)", "(8, 'I', 'I', None)"]
+    out = trav.depth_first_search(order='out_order')
+    assert [str(n) for n in out] == \
+    ["(8, 'I', 'I', None)", "(None, 'H', 'H', None)", "(None, 'G', 'G', 7)",
+     "(1, 'F', 'F', 3)", "(None, 'E', 'E', None)", "(5, 'D', 'D', 6)",
+     "(None, 'C', 'C', None)", "(2, 'B', 'B', 4)", "(None, 'A', 'A', None)"]
+    post = trav.depth_first_search(order='post_order')
+    assert [str(n) for n in post] == \
+    ["(None, 'A', 'A', None)", "(None, 'C', 'C', None)",
+     "(None, 'E', 'E', None)", "(5, 'D', 'D', 6)", "(2, 'B', 'B', 4)",
+     "(None, 'H', 'H', None)", "(8, 'I', 'I', None)", "(None, 'G', 'G', 7)",
+     "(1, 'F', 'F', 3)"]
+    bfs = trav.breadth_first_search()
+    assert [str(n) for n in bfs] == \
+        ["(1, 'F', 'F', 3)", "(2, 'B', 'B', 4)", "(None, 'G', 'G', 7)",
+         "(None, 'A', 'A', None)", "(5, 'D', 'D', 6)", "(8, 'I', 'I', None)",
+         "(None, 'C', 'C', None)", "(None, 'E', 'E', None)",
+         "(None, 'H', 'H', None)"]
+    raises(NotImplementedError, lambda: trav.breadth_first_search(strategy='iddfs'))
+    raises(NotImplementedError, lambda: trav.depth_first_search(order='in_out_order'))