Merge branch 'master' of git://github.com/TheAlgorithms/Python

Author: qckzr

Diff for: .travis.yml

@@ -6,31 +6,17 @@ before_install: pip install --upgrade pip setuptools
 install: pip install -r requirements.txt
 before_script:
   - black --check . || true
-  - flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+  - flake8 . --count --select=E9,F401,F63,F7,F82 --show-source --statistics
 script:
+  - scripts/validate_filenames.py  # no uppercase and no spaces
   - mypy --ignore-missing-imports .
-  #- IGNORE="data_structures,file_transfer_protocol,graphs,machine_learning,maths,neural_network,project_euler"
-  #- pytest . --doctest-modules --ignore=${IGNORE}
-  - pytest --doctest-modules
-      arithmetic_analysis
-      backtracking
-      boolean_algebra
-      ciphers
-      compression
-      conversions
-      digital_image_processing
-      divide_and_conquer
-      dynamic_programming
-      hashes
-      linear_algebra_python
-      matrix
-      networking_flow
-      other
-      searches
-      sorts
-      strings
-      traversals
-
+  - pytest . --doctest-modules
+      --ignore=file_transfer_protocol/ftp_send_receive.py
+      --ignore=file_transfer_protocol/ftp_client_server.py
+      --ignore=machine_learning/linear_regression.py
+      --ignore=machine_learning/perceptron.py
+      --ignore=machine_learning/random_forest_classification/random_forest_classification.py
+      --ignore=machine_learning/random_forest_regression/random_forest_regression.py
 after_success:
-  - python scripts/build_directory_md.py
+  - scripts/build_directory_md.py > DIRECTORY.md
   - cat DIRECTORY.md

Diff for: CONTRIBUTING.md

@@ -69,7 +69,7 @@ We want your work to be readable by others; therefore, we encourage you to note
       """
   	This function sums two integers a and b
   	Return: a + b
-  	"""
+      """
       return a + b
   ```
 

Diff for: DIRECTORY.md

@@ -1,9 +1,11 @@
 # 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)
-
+[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg?logo=paypal&style=flat-square)](https://www.paypal.me/TheAlgorithms/100)&nbsp;
+[![Build Status](https://img.shields.io/travis/TheAlgorithms/Python.svg?label=Travis%20CI&logo=travis&style=flat-square)](https://travis-ci.org/TheAlgorithms/Python)&nbsp;
+[![LGTM](https://img.shields.io/lgtm/alerts/github/TheAlgorithms/Python.svg?label=LGTM&logo=LGTM&style=flat-square)](https://lgtm.com/projects/g/TheAlgorithms/Python/alerts)&nbsp;
+[![Gitter chat](https://img.shields.io/badge/Chat-Gitter-ff69b4.svg?label=Chat&logo=gitter&style=flat-square)](https://gitter.im/TheAlgorithms)&nbsp;
+[![contributions welcome](https://img.shields.io/static/v1.svg?label=Contributions&message=Welcome&color=0059b3&style=flat-square)](https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md)&nbsp;
+![](https://img.shields.io/github/repo-size/TheAlgorithms/Python.svg?label=Repo%20size&style=flat-square)&nbsp;
+<!--[![Tested on Python 3.7](https://img.shields.io/badge/Tested%20-Python%203.7-blue.svg?logo=python&style=flat-square)]( https://www.python.org/downloads) &nbsp;-->
 ### All algorithms implemented in Python (for education)
 
 These implementations are for learning purposes. They may be less efficient than the implementations in the Python standard library.
@@ -24,6 +26,8 @@ Chetan Kaushik
 
 Read our [Contribution Guidelines](CONTRIBUTING.md) before you contribute.
 
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg?style=flat-square)](https://gitpod.io/#https://github.com/TheAlgorithms/Python)
+
 ## Community Channel
 
 We're on [Gitter](https://gitter.im/TheAlgorithms)! Please join us.

Diff for: README.md

@@ -0,0 +1,89 @@
+"""
+Checks if a system of forces is in static equilibrium.
+
+python/black : true
+flake8 : passed
+mypy : passed
+"""
+
+from numpy import array, cos, sin, radians, cross  # type: ignore
+from typing import List
+
+
+def polar_force(
+    magnitude: float, angle: float, radian_mode: bool = False
+) -> List[float]:
+    """
+    Resolves force along rectangular components.
+    (force, angle) => (force_x, force_y)
+    >>> polar_force(10, 45)
+    [7.0710678118654755, 7.071067811865475]
+    >>> polar_force(10, 3.14, radian_mode=True)
+    [-9.999987317275394, 0.01592652916486828]
+    """
+    if radian_mode:
+        return [magnitude * cos(angle), magnitude * sin(angle)]
+    return [magnitude * cos(radians(angle)), magnitude * sin(radians(angle))]
+
+
+def in_static_equilibrium(
+    forces: array, location: array, eps: float = 10 ** -1
+) -> bool:
+    """
+    Check if a system is in equilibrium.
+    It takes two numpy.array objects.
+    forces ==>  [
+                        [force1_x, force1_y],
+                        [force2_x, force2_y],
+                        ....]
+    location ==>  [
+                        [x1, y1],
+                        [x2, y2],
+                        ....]
+    >>> force = array([[1, 1], [-1, 2]])
+    >>> location = array([[1, 0], [10, 0]])
+    >>> in_static_equilibrium(force, location)
+    False
+    """
+    # summation of moments is zero
+    moments: array = cross(location, forces)
+    sum_moments: float = sum(moments)
+    return abs(sum_moments) < eps
+
+
+if __name__ == "__main__":
+    # Test to check if it works
+    forces = array(
+        [
+            polar_force(718.4, 180 - 30),
+            polar_force(879.54, 45),
+            polar_force(100, -90)
+        ])
+
+    location = array([[0, 0], [0, 0], [0, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    # Problem 1 in image_data/2D_problems.jpg
+    forces = array(
+        [
+            polar_force(30 * 9.81, 15),
+            polar_force(215, 180 - 45),
+            polar_force(264, 90 - 30),
+        ]
+    )
+
+    location = array([[0, 0], [0, 0], [0, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    # Problem in image_data/2D_problems_1.jpg
+    forces = array([[0, -2000], [0, -1200], [0, 15600], [0, -12400]])
+
+    location = array([[0, 0], [6, 0], [10, 0], [12, 0]])
+
+    assert in_static_equilibrium(forces, location)
+
+    import doctest
+
+    doctest.testmod()

Diff for: arithmetic_analysis/image_data/2D_problems.JPG

@@ -1,5 +1,5 @@
 # Implementing Newton Raphson method in Python
-# Author: Haseeb
+# Author: Syed Haseeb Shah (github.com/QuantumNovice)
 
 from sympy import diff
 from decimal import Decimal
@@ -30,7 +30,3 @@ def NewtonRaphson(func, a):
 
     # Exponential Roots
     print ('exp(x) - 1 = 0', NewtonRaphson('exp(x) - 1', 0))
-    
-    
-    
-

Diff for: arithmetic_analysis/image_data/2D_problems_1.JPG

@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+
+"""
+	In this problem, we want to determine all possible combinations of k
+	numbers out of 1 ... n. We use backtracking to solve this problem.
+	Time complexity: O(C(n,k)) which is O(n choose k) = O((n!/(k! * (n - k)!)))
+"""
+
+
+def generate_all_combinations(n: int, k: int) -> [[int]]:
+    """
+    >>> generate_all_combinations(n=4, k=2)
+    [[1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4]]
+    """
+    
+    result = []
+    create_all_state(1, n, k, [], result)
+    return result
+
+
+def create_all_state(increment, total_number, level, current_list, total_list):
+    if level == 0:
+        total_list.append(current_list[:])
+        return
+
+    for i in range(increment, total_number - level + 2):
+        current_list.append(i)
+        create_all_state(i + 1, total_number, level - 1, current_list, total_list)
+        current_list.pop()
+
+
+def print_all_state(total_list):
+    for i in total_list:
+        print(*i)
+
+
+if __name__ == '__main__':
+    n = 4
+    k = 2
+    total_list = generate_all_combinations(n, k)
+    print_all_state(total_list)