Merge branch 'master' of https://github.com/TheAlgorithms/Python into issue#817

Author: Dharni0607

.github/FUNDING.yml

@@ -0,0 +1,12 @@
+# These are supported funding model platforms
+
+github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+patreon: # Replace with a single Patreon username
+open_collective: # Replace with a single Open Collective username
+ko_fi: # Replace with a single Ko-fi username
+tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
+community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
+liberapay: TheAlgorithms
+issuehunt: # Replace with a single IssueHunt username
+otechie: # Replace with a single Otechie username
+custom: ['http://paypal.me/TheAlgorithms/1000', 'https://donorbox.org/thealgorithms']

.lgtm.yml

@@ -1,26 +1,14 @@
 language: python
+dist: xenial  # required for Python >= 3.7
+python: 3.7
 cache: pip
-python:
-    - 2.7
-    - 3.6
-    #- nightly
-    #- pypy
-    #- pypy3
-matrix:
-    allow_failures:
-        - python: nightly
-        - python: pypy
-        - python: pypy3
-install:
-    #- pip install -r requirements.txt
-    - pip install flake8  # pytest  # add another testing frameworks later
+install: pip install -r requirements.txt
 before_script:
-    # stop the build if there are Python syntax errors or undefined names
-    - flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics
-    # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide
-    - flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+  - black --check . || true
+  - flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
 script:
-    - true  # pytest --capture=sys  # add other tests here
-notifications:
-    on_success: change
-    on_failure: change  # `always` will be the setting once code changes slow down
+  - mypy --ignore-missing-imports .
+  - pytest --doctest-modules ./ciphers ./other ./searches ./sorts ./strings
+after_success:
+  - python ./~script.py
+  - cat DIRECTORY.md

.travis.yml

@@ -28,6 +28,13 @@ We appreciate any contribution, from fixing a grammar mistake in a comment to im
 We want your work to be readable by others; therefore, we encourage you to note the following:
 
 - Please write in Python 3.x.
+- Please consider running [__python/black__](https://github.com/python/black) on your Python file(s) before submitting your pull request.  This is not a requirement but it does make your code more readable.  There are other code formatters (autopep8, yapf) but the __black__ style is now the recommendation of the Python core team. To use it,
+    ```bash
+    pip3 install black  # only required the first time
+    black my-submission.py
+    ```
+
+- All submissions will need to pass the test __flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics__ before they will be accepted so if possible, try this test locally on your Python file(s) before submitting your pull request.
 
 - If you know [PEP 8](https://www.python.org/dev/peps/pep-0008/) already, you will have no problem in coding style, though we do not follow it strictly. Read the remaining section and have fun coding!
 
@@ -72,13 +79,19 @@ We want your work to be readable by others; therefore, we encourage you to note
 
 - Write tests to illustrate your work.
 
-  The following "testing" approaches are not encouraged:
+  The following "testing" approaches are **not** encouraged:
 
   ```python
   input('Enter your input:') 
   # Or even worse...
   input = eval(raw_input("Enter your input: "))
   ```
+  
+  However, if your code uses __input()__ then we encourage you to gracefully deal with leading and trailing whitespace in user input by adding __.strip()__ to the end as in:
+  
+  ```python
+  starting_value = int(input("Please enter a starting value: ").strip())
+  ```
 
   Please write down your test case, like the following:
 
@@ -92,30 +105,32 @@ We want your work to be readable by others; therefore, we encourage you to note
   print("1 + 2 = ", sumab(1,2))	# 1+2 = 3
   print("6 + 4 = ", sumab(6,4))	# 6+4 = 10
   ```
+  
+  Better yet, if you know how to write [__doctests__](https://docs.python.org/3/library/doctest.html), please consider adding them.
 
-- Avoid importing external libraries for basic algorithms. Use those libraries for complicated algorithms.
+- Avoid importing external libraries for basic algorithms. Only use those libraries for complicated algorithms.
 
 #### Other Standard While Submitting Your Work
 
-- File extension for code should be `.py`.
+- File extension for code should be `.py`. Jupiter notebook files are acceptable in machine learning algorithms.
 
-- Please file your work to let others use it in the future. Here are the examples that are acceptable:
-
-  - Camel cases
-  - `-` Hyphenated names
-  - `_` Underscore-separated names
+- Strictly use snake case (underscore separated) in your file name, as it will be easy to parse in future using scripts.
 
   If possible, follow the standard *within* the folder you are submitting to.
 
 - If you have modified/added code work, make sure the code compiles before submitting.
 
-- If you have modified/added documentation work, make sure your language is concise and contains no grammar mistake.
+- If you have modified/added documentation work, ensure your language is concise and contains no grammar errors.
+
+- Do not update the README.md or DIRECTORY.md file which will be periodically autogenerated by our Travis CI processes.
 
 - Add a corresponding explanation to [Algorithms-Explanation](https://github.com/TheAlgorithms/Algorithms-Explanation) (Optional but recommended).
 
+- All submissions will be tested with [__mypy__](http://www.mypy-lang.org) so we encourage to add [__Python type hints__](https://docs.python.org/3/library/typing.html) where it makes sense to do so.
+
 - Most importantly,
 
-  - **Be consistent with this guidelines while submitting.**
+  - **Be consistent in the use of these guidelines when submitting.**
   - **Join** [Gitter](https://gitter.im/TheAlgorithms) **now!**
   - Happy coding!
 

CONTRIBUTING.md

@@ -1,6 +1,3 @@
-## Analysis
-  * Compression Analysis
-    * [psnr](https://github.com/TheAlgorithms/Python/blob/master/analysis/compression_analysis/psnr.py)
 ## Arithmetic Analysis
   * [bisection](https://github.com/TheAlgorithms/Python/blob/master/arithmetic_analysis/bisection.py)
   * [intersection](https://github.com/TheAlgorithms/Python/blob/master/arithmetic_analysis/intersection.py)
@@ -39,17 +36,19 @@
   * [xor cipher](https://github.com/TheAlgorithms/Python/blob/master/ciphers/xor_cipher.py)
 ## Compression
   * [huffman](https://github.com/TheAlgorithms/Python/blob/master/compression/huffman.py)
+## Compression Analysis
+  * [psnr](https://github.com/TheAlgorithms/Python/blob/master/compression_analysis/psnr.py)
 ## Data Structures
   * [arrays](https://github.com/TheAlgorithms/Python/blob/master/data_structures/arrays.py)
   * [avl](https://github.com/TheAlgorithms/Python/blob/master/data_structures/avl.py)
   * [LCA](https://github.com/TheAlgorithms/Python/blob/master/data_structures/LCA.py)
   * Binary Tree
-    * [AVL tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/AVL_tree.py)
-    * [binary search tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/binary_search_tree.py)
-    * [fenwick tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/fenwick_tree.py)
-    * [lazy segment tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/lazy_segment_tree.py)
-    * [segment tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/segment_tree.py)
-    * [treap](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary%20tree/treap.py)
+    * [AVL tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/AVL_tree.py)
+    * [binary search tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/binary_search_tree.py)
+    * [fenwick tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/fenwick_tree.py)
+    * [lazy segment tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/lazy_segment_tree.py)
+    * [segment tree](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/segment_tree.py)
+    * [treap](https://github.com/TheAlgorithms/Python/blob/master/data_structures/binary_tree/treap.py)
   * Hashing
     * [double hash](https://github.com/TheAlgorithms/Python/blob/master/data_structures/hashing/double_hash.py)
     * [hash table](https://github.com/TheAlgorithms/Python/blob/master/data_structures/hashing/hash_table.py)
@@ -192,8 +191,9 @@
   * Tests
     * [test fibonacci](https://github.com/TheAlgorithms/Python/blob/master/maths/tests/test_fibonacci.py)
 ## Matrix
-  * [matrix multiplication addition](https://github.com/TheAlgorithms/Python/blob/master/matrix/matrix_multiplication_addition.py)
+  * [matrix operation](https://github.com/TheAlgorithms/Python/blob/master/matrix/matrix_operation.py)
   * [searching in sorted matrix](https://github.com/TheAlgorithms/Python/blob/master/matrix/searching_in_sorted_matrix.py)
+  * [spiralPrint](https://github.com/TheAlgorithms/Python/blob/master/matrix/spiralPrint.py)
 ## Networking Flow
   * [ford fulkerson](https://github.com/TheAlgorithms/Python/blob/master/networking_flow/ford_fulkerson.py)
   * [minimum cut](https://github.com/TheAlgorithms/Python/blob/master/networking_flow/minimum_cut.py)
@@ -294,6 +294,8 @@
     * [p022 names](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_22/p022_names.txt)
     * [sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_22/sol1.py)
     * [sol2](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_22/sol2.py)
+  * Problem 234
+    * [sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_234/sol1.py)
   * Problem 24
     * [sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_24/sol1.py)
   * Problem 25

DIRECTORY.md

@@ -1,4 +1,5 @@
 # The Algorithms - Python <!-- [![Build Status](https://travis-ci.org/TheAlgorithms/Python.svg)](https://travis-ci.org/TheAlgorithms/Python) -->
+
 [![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.me/TheAlgorithms/100) &nbsp;
 [![Gitter chat](https://badges.gitter.im/gitterHQ/gitter.png)](https://gitter.im/TheAlgorithms) &nbsp;
 [![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/TheAlgorithms/Python)
@@ -7,6 +8,17 @@
 
 These implementations are for learning purposes. They may be less efficient than the implementations in the Python standard library.
 
+## Owners
+
+Anup Kumar Panwar
+&nbsp; [[Gmail](mailto:[email protected]?Subject=The%20Algorithms%20-%20Python)
+&nbsp; [GitHub](https://github.com/anupkumarpanwar)
+&nbsp; [LinkedIn](https://www.linkedin.com/in/anupkumarpanwar/)]
+
+Chetan Kaushik
+&nbsp; [[Gmail](mailto:[email protected]?Subject=The%20Algorithms%20-%20Python)
+&nbsp; [GitHub](https://github.com/dynamitechetan)
+&nbsp; [LinkedIn](https://www.linkedin.com/in/chetankaushik/)]
 
 ## Contribution Guidelines
 
@@ -15,3 +27,7 @@ Read our [Contribution Guidelines](CONTRIBUTING.md) before you contribute.
 ## Community Channel
 
 We're on [Gitter](https://gitter.im/TheAlgorithms)! Please join us.
+
+## Algorithms
+
+See our [directory](DIRECTORY.md).

README.md

@@ -0,0 +1,45 @@
+'''
+	In this problem, we want to determine all possible permutations
+	of the given sequence. We use backtracking to solve this problem.
+
+	Time complexity: O(n! * n),
+	where n denotes the length of the given sequence.
+'''
+
+
+def generate_all_permutations(sequence):
+	create_state_space_tree(sequence, [], 0, [0 for i in range(len(sequence))])
+
+
+def create_state_space_tree(sequence, current_sequence, index, index_used):
+	'''
+	Creates a state space tree to iterate through each branch using DFS.
+	We know that each state has exactly len(sequence) - index children.
+	It terminates when it reaches the end of the given sequence.
+	'''
+
+	if index == len(sequence):
+		print(current_sequence)
+		return
+
+	for i in range(len(sequence)):
+		if not index_used[i]:
+			current_sequence.append(sequence[i])
+			index_used[i] = True
+			create_state_space_tree(sequence, current_sequence, index + 1, index_used)
+			current_sequence.pop()
+			index_used[i] = False
+
+
+'''
+remove the comment to take an input from the user 
+
+print("Enter the elements")
+sequence = list(map(int, input().split()))
+'''
+
+sequence = [3, 1, 2, 4]
+generate_all_permutations(sequence)
+
+sequence = ["A", "B", "C"]
+generate_all_permutations(sequence)

backtracking/all_permutations.py

@@ -0,0 +1,42 @@
+'''
+	In this problem, we want to determine all possible subsequences
+	of the given sequence. We use backtracking to solve this problem.
+
+	Time complexity: O(2^n),
+	where n denotes the length of the given sequence.
+'''
+
+
+def generate_all_subsequences(sequence):
+	create_state_space_tree(sequence, [], 0)
+
+
+def create_state_space_tree(sequence, current_subsequence, index):
+	'''
+	Creates a state space tree to iterate through each branch using DFS.
+	We know that each state has exactly two children.
+	It terminates when it reaches the end of the given sequence.
+	'''
+
+	if index == len(sequence):
+		print(current_subsequence)
+		return
+
+	create_state_space_tree(sequence, current_subsequence, index + 1)
+	current_subsequence.append(sequence[index])
+	create_state_space_tree(sequence, current_subsequence, index + 1)
+	current_subsequence.pop()
+
+
+'''
+remove the comment to take an input from the user 
+
+print("Enter the elements")
+sequence = list(map(int, input().split()))
+'''
+
+sequence = [3, 1, 2, 4]
+generate_all_subsequences(sequence)
+
+sequence = ["A", "B", "C"]
+generate_all_subsequences(sequence)

backtracking/all_subsequences.py

@@ -0,0 +1,28 @@
+import math 
+
+''' Minimax helps to achieve maximum score in a game by checking all possible moves
+    depth is current depth in game tree. 
+    nodeIndex is index of current node in scores[].
+    if move is of maximizer return true else false
+    leaves of game tree is stored in scores[]  
+    height is maximum height of Game tree
+'''
+
+def minimax (Depth, nodeIndex, isMax, scores, height):  
+
+    if Depth == height:  
+        return scores[nodeIndex] 
+
+    if isMax: 
+        return (max(minimax(Depth + 1, nodeIndex * 2, False, scores, height),
+                    minimax(Depth + 1, nodeIndex * 2 + 1, False, scores, height))) 
+    return (min(minimax(Depth + 1, nodeIndex * 2, True, scores, height), 
+               minimax(Depth + 1, nodeIndex * 2 + 1, True, scores, height))) 
+
+if __name__ == "__main__": 
+ 
+    scores = [90, 23, 6, 33, 21, 65, 123, 34423] 
+    height = math.log(len(scores), 2) 
+
+    print("Optimal value : ", end = "") 
+    print(minimax(0, 0, True, scores, height))