From 86dbf0a9d399c93280a9676ef3bf3cbc2fc2a284 Mon Sep 17 00:00:00 2001
From: faizan2700 <46817346+faizan2700@users.noreply.github.com>
Date: Wed, 18 Dec 2019 19:55:12 +0530
Subject: [PATCH] file iterating_through_submasks.py for given mask is added in
 dynamic_programming (#1635)

* new file *iterating_through_submasks* is added in dynamic_programming section

* no changes

* *iterating_through_submasks.py is added in dynamic_programming

* iterating_through_submasks is added with doctests

* iterating_through_submasks.py is added in dynamic_programming

* changes made in *iterating_through_submasks.py

* changes made in *iterating_through_submasks.py

* updated
---
 .../iterating_through_submasks.py             | 60 +++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 dynamic_programming/iterating_through_submasks.py

diff --git a/dynamic_programming/iterating_through_submasks.py b/dynamic_programming/iterating_through_submasks.py
new file mode 100644
index 000000000..edeacc312
--- /dev/null
+++ b/dynamic_programming/iterating_through_submasks.py
@@ -0,0 +1,60 @@
+"""
+Author : Syed Faizan (3rd Year Student IIIT Pune) 
+github : faizan2700
+You are given a bitmask m and you want to efficiently iterate through all of
+its submasks. The mask s is submask of m if only bits that were included in
+bitmask are set
+"""
+from typing import List
+
+
+def list_of_submasks(mask: int) -> List[int]:
+
+    """
+    Args:
+        mask : number which shows mask ( always integer > 0, zero does not have any submasks )
+
+    Returns:
+        all_submasks : the list of submasks of mask (mask s is called submask of mask
+        m if only bits that were included in original mask are set
+
+    Raises:
+        AssertionError: mask not positive integer
+
+    >>> list_of_submasks(15)
+    [15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
+    >>> list_of_submasks(13)
+    [13, 12, 9, 8, 5, 4, 1]
+    >>> list_of_submasks(-7)  # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+        ...
+    AssertionError: mask needs to be positive integer, your input -7
+    >>> list_of_submasks(0)  # doctest: +ELLIPSIS
+    Traceback (most recent call last):
+        ...
+    AssertionError: mask needs to be positive integer, your input 0
+    
+    """
+
+    fmt = "mask needs to be positive integer, your input {}"
+    assert isinstance(mask, int) and mask > 0, fmt.format(mask)
+
+    """
+    first submask iterated will be mask itself then operation will be performed
+    to get other submasks till we reach empty submask that is zero ( zero is not
+    included in final submasks list )
+    """
+    all_submasks = []
+    submask = mask
+
+    while submask:
+        all_submasks.append(submask)
+        submask = (submask - 1) & mask
+
+    return all_submasks
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()