Data commit

Task/M-bius-function/Nim/m-bius-function.nim

@@ -0,0 +1,53 @@
+import std/[math, sequtils, strformat]
+
+func getStep(n: int): int {.inline.} =
+  result = 1 + n shl 2 - n shr 1 shl 1
+
+func primeFac(n: int): seq[int] =
+  var
+    maxq = int(sqrt(float(n)))
+    d = 1
+    q: int = 2 + (n and 1)   # Start with 2 or 3 according to oddity.
+
+  while q <= maxq and n %% q != 0:
+    q = getStep(d)
+    inc d
+  if q <= maxq:
+    let q1 = primeFac(n /% q)
+    let q2 = primeFac(q)
+    result = concat(q2, q1, result)
+  else:
+    result.add(n)
+
+func squareFree(num: int): bool =
+  let fact = primeFac num
+
+  for i in fact:
+    if fact.count(i) > 1:
+      return false
+
+  return true
+
+func mobius(num: int): int =
+  if num == 1: return num
+
+  let fact = primeFac num
+
+  for i in fact:
+    ## check if it has a squared prime factor
+    if fact.count(i) == 2:
+      return 0
+
+  if num.squareFree:
+    if fact.len mod 2 == 0:
+      return 1
+    else:
+      return -1
+
+when isMainModule:
+  echo "The first 199 möbius numbers are:"
+
+  for i in 1..199:
+    stdout.write fmt"{mobius(i):4}"
+    if i mod 20 == 0:
+      echo "" # print newline