Added Dynamic Arrays (#28)

* added dynamic arrays

* removed python2.7

Author: czgdp1807

.travis.yml

@@ -3,7 +3,6 @@ sudo: false
 language: python
 
 python:
-        - "2.7"
         - "3.5"
 install:
         - pip install -r requirements.txt

pydatastructs/linear_data_structures/__init__.py

@@ -6,5 +6,6 @@
 
 from .arrays import (
     OneDimensionalArray,
+    DynamicOneDimensionalArray
 )
 __all__.extend(arrays.__all__)

pydatastructs/linear_data_structures/arrays.py

@@ -2,7 +2,8 @@
 from pydatastructs.utils.misc_util import _check_type, NoneType
 
 __all__ = [
-'OneDimensionalArray'
+'OneDimensionalArray',
+'DynamicOneDimensionalArray'
 ]
 
 class Array(object):
@@ -112,3 +113,129 @@ def fill(self, elem):
         elem = self._dtype(elem)
         for i in range(self._size):
             self._data[i] = elem
+
+ODA = OneDimensionalArray
+
+class DynamicArray(Array):
+    """
+    Abstract class for dynamic arrays.
+    """
+    pass
+
+class DynamicOneDimensionalArray(DynamicArray, OneDimensionalArray):
+    """
+    Represents dynamic one dimensional arrays.
+
+    Parameters
+    ==========
+
+    dtype: type
+        A valid object type.
+    size: int
+        The number of elements in the array.
+    elements: list/tuple
+        The elements in the array, all should
+        be of same type.
+    init: a python type
+        The inital value with which the element has
+        to be initialized. By default none, used only
+        when the data is not given.
+    load_factor: float, by default 0.25
+        The number below which if the ratio, Num(T)/Size(T)
+        falls then the array is contracted such that at
+        most only half the positions are filled.
+
+    Raises
+    ======
+
+    ValueError
+        When the number of elements in the list do not
+        match with the size.
+        More than three parameters are passed as arguments.
+        Types of arguments is not as mentioned in the docstring.
+        The load factor is not of floating point type.
+
+    Note
+    ====
+
+    At least one parameter should be passed as an argument along
+    with the dtype.
+    Num(T) means the number of positions which are not None in the
+    array.
+    Size(T) means the maximum number of elements that the array can hold.
+
+    Examples
+    ========
+
+    >>> from pydatastructs import DynamicOneDimensionalArray as DODA
+    >>> arr = DODA(int, 0)
+    >>> arr.append(1)
+    >>> arr.append(2)
+    >>> arr[0]
+    1
+    >>> arr.delete(0)
+    >>> arr[0]
+    >>> arr[1]
+    2
+    >>> arr.append(3)
+    >>> arr.append(4)
+    >>> [arr[i] for i in range(arr.size)]
+    [None, 2, 3, 4, None, None, None]
+
+    References
+    ==========
+
+    .. [1] http://www.cs.nthu.edu.tw/~wkhon/algo09/lectures/lecture16.pdf
+    """
+
+    __slots__ = ['_load_factor', '_num', '_last_pos_filled', '_size']
+
+    def __new__(cls, dtype=NoneType, *args, **kwargs):
+        obj = super().__new__(cls, dtype, *args, **kwargs)
+        obj._load_factor = float(kwargs.get('load_factor', 0.25))
+        obj._num = 0 if obj._size == 0 or obj[0] == None else obj._size
+        obj._last_pos_filled = obj._num - 1
+        return obj
+
+    def _modify(self):
+        """
+        Contracts the array if Num(T)/Size(T) falls
+        below load factor.
+        """
+        if self._num/self._size < self._load_factor:
+            arr_new = ODA(self._dtype, 2*self._num + 1)
+            j = 0
+            for i in range(self._last_pos_filled + 1):
+                if self[i] != None:
+                    arr_new[j] = self[i]
+                    j += 1
+            self._last_pos_filled = j - 1
+            self._data = arr_new._data
+            self._size = arr_new._size
+
+    def append(self, el):
+        if self._last_pos_filled + 1 == self._size:
+            arr_new = ODA(self._dtype, 2*self._size + 1)
+            for i in range(self._last_pos_filled + 1):
+                arr_new[i] = self[i]
+            arr_new[self._last_pos_filled + 1] = el
+            self._last_pos_filled += 1
+            self._size = arr_new._size
+            self._num += 1
+            self._data = arr_new._data
+        else:
+            self[self._last_pos_filled + 1] = el
+            self._last_pos_filled += 1
+            self._num += 1
+        self._modify()
+
+    def delete(self, idx):
+        if idx <= self._last_pos_filled and idx >= 0 and \
+            self[idx] != None:
+            self[idx] = None
+            self._num -= 1
+            self._modify()
+
+    @property
+    def size(self):
+        return self._size

pydatastructs/linear_data_structures/tests/test_arrays.py

@@ -1,4 +1,5 @@
-from pydatastructs.linear_data_structures import OneDimensionalArray
+from pydatastructs.linear_data_structures import (
+    OneDimensionalArray, DynamicOneDimensionalArray)
 from pydatastructs.utils.raises_util import raises
 
 
@@ -17,3 +18,21 @@ def test_OneDimensionalArray():
     raises(TypeError, lambda: ODA(int, 5.0))
     raises(TypeError, lambda: ODA(int, set([1, 2, 3])))
     raises(ValueError, lambda: ODA(int, 3, [1]))
+
+def test_DynamicOneDimensionalArray():
+    DODA = DynamicOneDimensionalArray
+    A = DODA(int, 0)
+    A.append(1)
+    A.append(2)
+    A.append(3)
+    A.append(4)
+    A.delete(0)
+    A.delete(0)
+    A.delete(15)
+    A.delete(-1)
+    A.delete(1)
+    A.delete(2)
+    assert A._data == [4, None, None]
+    assert A.size == 3
+    A.fill(4)
+    assert A._data == [4, 4, 4]