Data commit

Task/Goldbachs-comet/Nim/goldbachs-comet.nim

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+import std/[math, strformat, strutils, sugar]
+import chroma, plotly
+
+const
+  N1 = 100        # For part 1 of task.
+  N2 = 1_000_000  # For part 2 of task.
+  N3 = 2000       # For stretch part.
+
+# Erathostenes sieve.
+var isPrime: array[1..N1, bool]
+for i in 2..N1: isPrime[i] = true
+for n in 2..sqrt(N1.toFloat).int:
+  for k in countup(n * n, N1, n):
+    isPrime[k] = false
+
+proc g(n: int): int =
+  ## Goldbach function.
+  assert n > 2 and n mod 2 == 0, "“n” must be even and greater than 2."
+  for i in 1..(n div 2):
+    if isPrime[i] and isPrime[n - i]:
+      inc result
+
+# Part 1.
+echo &"First {N1} G numbers:"
+var col = 1
+for n in 2..N1:
+  stdout.write align($g( 2 * n), 3)
+  stdout.write if col mod 10 == 0: '\n' else: ' '
+  inc col
+
+# Part 2.
+echo &"\nG({N2}) = ", g(N2)
+
+# Stretch part.
+
+const Colors = collect(for name in ["red", "blue", "green"]: name.parseHtmlName())
+var x, y: seq[float]
+var colors: seq[Color]
+for n in 2..N3:
+  x.add n.toFloat
+  y.add g(2 * n).toFloat
+  colors.add Colors[n mod 3]
+
+let trace = Trace[float](type: Scatter, mode: Markers, marker: Marker[float](color: colors), xs: x, ys: y)
+let layout = Layout(title: "Goldbach’s comet", width: 1200, height: 400)
+Plot[float64](layout: layout, traces: @[trace]).show(removeTempFile = true)