From 6aa5c270464f36c0fb846c3dfd8b95db8dc2fa66 Mon Sep 17 00:00:00 2001
From: Mohammad S Anwar <mohammad.anwar@yahoo.com>
Date: Tue, 5 Apr 2022 21:25:55 +0100
Subject: - Added guest contributions by Eric Cheung.

---
 challenge-159/eric-cheung/python/ch-1.py | 65 +++++++++++++++++++++++++++++
 challenge-159/eric-cheung/python/ch-2.py | 70 ++++++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+)
 create mode 100755 challenge-159/eric-cheung/python/ch-1.py
 create mode 100755 challenge-159/eric-cheung/python/ch-2.py

diff --git a/challenge-159/eric-cheung/python/ch-1.py b/challenge-159/eric-cheung/python/ch-1.py
new file mode 100755
index 0000000000..84e4d54b07
--- /dev/null
+++ b/challenge-159/eric-cheung/python/ch-1.py
@@ -0,0 +1,65 @@
+## Remarks
+## https://www.geeksforgeeks.org/farey-sequence/
+
+## Python3 program to print
+## Farey Sequence of given order
+
+## Class for fraction x / y (a term in farey sequence)
+class Term:
+
+    ## Constructor to initialize
+    ## x and y in x / y
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+
+## GCD of a and b
+def gcd(a, b):
+    if b == 0:
+        return a
+
+    return gcd(b, a % b)
+
+## Function to print
+## Farey sequence of order n
+def farey(n):
+
+    ## Create a vector to store terms of output
+    v = []
+
+    ## One by one find and store all terms except 0 / 1 and n / n which are known
+    for i in range(1, n + 1):
+        for j in range(i + 1, n + 1):
+
+            ## Checking whether i and j are in lowest term
+            if gcd(i, j) == 1:
+                v.append(Term(i, j))
+
+    ## Sorting the term of sequence
+    for i in range(len(v)):
+        for j in range(i + 1, len(v)):
+            if (v[i].x * v[j].y > v[j].x * v[i].y):
+                v[i], v[j] = v[j], v[i]
+
+    ## Explicitly printing first term
+    print("0 / 1", end = " ")
+
+	## Printing other terms
+    for i in range(len(v)):
+        print("%d/%d" % (v[i].x, v[i].y), end = " ")
+
+	## explicitly printing last term
+    print("1/1")
+
+
+# Driver Code
+if __name__ == "__main__":
+    ## n = 5 ## Example 1:
+    ## n = 7 ## Example 2:
+    n = 4 ## Example 3:
+
+    print("Farey sequence of order %d is" % n)
+    farey(n)
+
+## This code is contributed by sanjeev2552
diff --git a/challenge-159/eric-cheung/python/ch-2.py b/challenge-159/eric-cheung/python/ch-2.py
new file mode 100755
index 0000000000..4e19c591df
--- /dev/null
+++ b/challenge-159/eric-cheung/python/ch-2.py
@@ -0,0 +1,70 @@
+## Remarks
+## https://www.geeksforgeeks.org/program-mobius-function/
+
+## Python program to evaluate
+## Mobius def M(N) = 1 if N = 1
+## M(N) = 0 if any prime factor of N is contained twice
+## M(N) = (-1) ^ (no of distinct prime factors)
+
+
+import math
+
+
+## def to check if n is prime or not
+def isPrime(n) :
+
+    if (n < 2) :
+        return False
+
+    for i in range(2, n + 1) :
+        if (n % i == 0) :
+            return False
+ 
+        i = i * i
+ 
+    return True
+
+
+def mobius(n) :
+
+    p = 0
+
+	## Handling 2 separately
+    if (n % 2 == 0) :
+
+        n = int(n / 2)
+        p = p + 1
+
+        ## If 2^2 also divides N
+        if (n % 2 == 0) :
+            return 0
+
+    ## Check for all other prime factors
+    for i in range(3, int(math.sqrt(n)) + 1) :
+
+        ## If i divides n
+        if (n % i == 0) :
+
+            n = int(n / i)
+            p = p + 1
+
+            ## If i ^ 2 also divides N
+            if (n % i == 0) :
+                return 0
+
+        i = i + 2
+
+    if(p % 2 == 0) :
+        return -1
+
+    return 1
+
+## Driver Code
+## N = 5 ## Example: 1
+## N = 10 ## Example: 2
+N = 20 ## Example: 3
+
+print ("Mobius defs M(N) at N = {} is: {}\n" . format(N, mobius(N)));
+
+							
+## This code is contributed by Manish Shaw (manishshaw1)
-- 
cgit