Create and populate the Maths directory (#4)

* Add a sample of maths basic algorithms

* Update maths/abs.nim

Co-authored-by: Zoom <[email protected]>

* Use openArray in absMaxSort

Co-authored-by: Zoom <[email protected]>

* Fix seq->openArray and int->SomeInteger

* Use Positive as input instead

* Update maths/addition_without_arithmetic.nim

Co-authored-by: Pietro Peterlongo <[email protected]>

* Name allocation number

* [maths/abs] Replace maxAbsSort by signed[Min/Max]Abs

* [Aliquot Sum] Add header

* Add empty line at end of file

* Remove Allocation number since it is a non standard algorithm

* Fix titles

* Run nimpretty on the files

* Rename file and add DIRECTORY.md

* abs: Fix variable name

* Add export marker

Co-authored-by: Zoom <[email protected]>

* Add RE block in aliquot sum and improve RE

Co-authored-by: Zoom <[email protected]>

* Remove MD quotation marks for inline code

* Add export marker for RE block

* Remove extra ValueError

---------

Co-authored-by: Dimitri LESNOFF <[email protected]>
Co-authored-by: Zoom <[email protected]>
Co-authored-by: Pietro Peterlongo <[email protected]>
Co-authored-by: David Leal <[email protected]>

Author: 4 people

DIRECTORY.md

@@ -6,6 +6,11 @@
   * [Catalan Numbers](dynamic_programming/catalan_numbers.nim)
   * [Viterbi](dynamic_programming/viterbi.nim)
 
+## Maths
+  * [Absolute value](maths/abs.nim)
+  * [Aliquot sum](maths/aliquot_sum.nim)
+  * [Bitwise Addition](maths/bitwise_addition.nim)
+
 ## Strings
   * [Check Anagram](strings/check_anagram.nim)
 

maths/abs.nim

@@ -0,0 +1,120 @@
+## Absolute value
+{.push raises: [].}
+import std/strutils
+
+runnableExamples:
+  assert absVal(-5.1) == 5.1
+  assert absMin(@[-1, 2, -3]) == 1
+  assert absMax(@[-1, 2, -3]) == 3
+  assert signedMinAbs(@[3, -10, -2]) == -2
+  assert signedMaxAbs(@[3, -10, -2]) == -10
+
+func absVal*[T: SomeFloat](num: T): T =
+  ## Returns the absolute value of a number.
+  ## Use `math.abs <https://nim-lang.org/docs/system.html#abs%2CT>`_ instead!
+  return if num < 0.0: -num else: num
+
+# Same for Integers but returns a Natural
+func absVal*[T: SomeInteger](num: T): Natural = (if num < 0: -num else: num)
+
+func absMin*(x: openArray[int]): Natural {.raises: [ValueError].} =
+  ## Returns the smallest element in absolute value in a sequence.
+  if x.len == 0:
+    raise newException(ValueError, """Cannot find absolute minimum
+     of an empty sequence""".unindent)
+  result = absVal(x[0])
+  for i in 1 ..< x.len:
+    if absVal(x[i]) < result:
+      result = absVal(x[i])
+
+func absMax*(x: openArray[int]): Natural {.raises: [ValueError].} =
+  ## Returns the largest element in absolute value in a sequence.
+  if x.len == 0:
+    raise newException(ValueError, """Cannot find absolute maximum of an empty
+   sequence""".unindent)
+  result = absVal(x[0])
+  for i in 1 ..< x.len:
+    if absVal(x[i]) > result:
+      result = absVal(x[i])
+
+func signedMinAbs*(x: openArray[int]): int {.raises: [ValueError].} =
+  ## Returns the first signed element whose absolute value
+  ## is the smallest in a sequence.
+  if x.len == 0:
+    raise newException(ValueError, """Cannot find absolute maximum of an empty
+   sequence""".unindent)
+  var (min, minAbs) = (x[0], absVal(x[0]))
+  for n in x:
+    let nAbs = absVal(n)
+    if nAbs < minAbs: (min, minAbs) = (n, nAbs)
+  min
+
+func signedMaxAbs*(x: openArray[int]): int {.raises: [ValueError].} =
+  ## Returns the first signed element whose absolute value
+  ## is the largest in a sequence.
+  if x.len == 0:
+    raise newException(ValueError, """Cannot find absolute maximum of an empty
+   sequence""".unindent)
+  var (max, maxAbs) = (x[0], absVal(x[0]))
+  for n in x:
+    let nAbs = absVal(n)
+    if nAbs > maxAbs: (max, maxAbs) = (n, nAbs)
+  max
+
+when isMainModule:
+  import std/[unittest, random]
+  randomize()
+
+  suite "Check absVal":
+    test "Check absVal":
+      check:
+        absVal(11.2) == 11.2
+        absVal(5) == 5
+        absVal(-5.1) == 5.1
+        absVal(-5) == absVal(5)
+        absVal(0) == 0
+
+  suite "Check absMin":
+    test "Check absMin":
+      check:
+        absMin(@[-1, 2, -3]) == 1
+        absMin(@[0, 5, 1, 11]) == 0
+        absMin(@[3, -10, -2]) == 2
+        absMin([-1, 2, -3]) == 1
+        absMin([0, 5, 1, 11]) == 0
+        absMin([3, -10, -2]) == 2
+
+    test "absMin on empty sequence raises ValueError":
+      doAssertRaises(ValueError):
+        discard absMin(@[])
+
+  suite "Check absMax":
+    test "Check absMax":
+      check:
+        absMax(@[0, 5, 1, 11]) == 11
+        absMax(@[3, -10, -2]) == 10
+        absMax(@[-1, 2, -3]) == 3
+
+    test "`absMax` on empty sequence raises ValueError":
+      doAssertRaises(ValueError):
+        discard absMax(@[])
+
+  suite "Check signedMinAbs":
+    test "Check signedMinAbs":
+      check:
+        signedMinAbs(@[0, 5, 1, 11]) == 0
+        signedMinAbs(@[3, -2, 1, -4, 5, -6]) == 1
+        signedMinAbs(@[3, -2, -1, -4, 5, -6]) == -1
+
+    test "Among two minimal elements, the first one is returned":
+      check signedMinAbs(@[3, -2, 1, -4, 5, -6, -1]) == 1
+
+  suite "Check signedMaxAbs":
+    test "Check signedMaxAbs":
+      check:
+        signedMaxAbs(@[3, -2, 1, -4, 5, -6]) == -6
+        signedMaxAbs(@[0, 5, 1, 11]) == 11
+
+    test "signedMaxAbs on empty sequence raises ValueError":
+      doAssertRaises(ValueError):
+        discard signedMaxAbs(@[])

maths/aliquot_sum.nim

@@ -0,0 +1,31 @@
+## Aliquot sum
+## In number theory, the aliquot sum s(n) of a positive integer n is the sum of
+## all proper divisors of n, that is, all divisors of n other than n itself.
+## https://en.wikipedia.org/wiki/Aliquot_sum
+
+runnableExamples:
+  import std/strformat
+  const expected = [16, 117]
+  for i, number in [12, 100].pairs():
+    let sum = aliquotSum(number)
+    assert sum == expected[i]
+    echo fmt"The sum of all the proper divisors of {number} is {sum}"
+
+func aliquotSum*(number: Positive): Natural =
+  ## Returns the sum of all the proper divisors of the number
+  ## Example: aliquotSum(12) = 1 + 2 + 3 + 4 + 6 = 16
+  result = 0
+  for divisor in 1 .. (number div 2):
+    if number mod divisor == 0:
+      result += divisor
+
+when isMainModule:
+  import std/unittest
+  suite "Check aliquotSum":
+    test "aliquotSum on small values":
+      var
+        input = @[1, 2, 9, 12, 27, 100]
+        expected = @[0, 1, 4, 16, 13, 117]
+      for i in 0 ..< input.len:
+        check:
+          aliquotSum(input[i]) == expected[i]

maths/bitwise_addition.nim

@@ -0,0 +1,38 @@
+## Bitwise Addition
+## Illustrate how to implement addition of integers using bitwise operations
+## See https://en.wikipedia.org/wiki/Bitwise_operation#Applications
+runnableExamples:
+  import std/strformat
+  var
+    a = 5
+    b = 6
+  echo fmt"The sum of {a} and {b} is {add(a,b)}"
+
+func add*(first: int, second: int): int =
+  ## Implementation of addition of integer with `and`, `xor` and `shl`
+  ## boolean operators.
+  var first = first
+  var second = second
+  while second != 0:
+    var c = first and second
+    first = first xor second
+    second = c shl 1
+  return first
+
+when isMainModule:
+  import std/unittest
+
+  suite "Check addition":
+    test "Addition of two positive numbers":
+      check:
+        add(3, 5) == 8
+        add(13, 5) == 18
+    test "Addition of two negative numbers":
+      check:
+        add(-7, -2) == -9
+        add(-321, -0) == -321
+    test "Addition of one positive and one negative number":
+      check:
+        add(-7, 2) == -5
+        add(-13, 5) == -8
+        add(13, -5) == 8