Add improved day8 code

day8/p2improved.nim

@@ -0,0 +1,79 @@
+import os, math
+import std/[strutils, sequtils]
+
+type
+  Segment = enum sA, sB, sC, sD, sE, sF, sG
+  Digit = set[Segment]
+
+func toDigit(chars: string): Digit =
+  chars.mapIt(Segment(ord(it) - ord('a'))).foldl(a + Digit({b}), Digit({}))
+
+proc main() =
+  let fileName = paramStr(1)
+
+  # The main idea here is to use process of elimination to find each number
+  # uniquely. To do this, we can use sets to eliminate or isolate numbers
+  # that we don't know. Inspired by:
+  # https://github.com/ZoomRmc/aoc2021_nim/blob/main/src/aoc08.nim
+
+  var sum = 0
+
+  const maxSetSize = 2^(Segment.high.int + 1)
+
+  for line in fileName.lines:
+    let
+      lineSplit = line.split(" | ")
+    var
+      digitMap: array[maxSetSize, int]
+      allDigits = lineSplit[0].strip().splitWhitespace().map(toDigit)
+      displayDigits = lineSplit[1].strip().splitWhitespace().map(toDigit)
+
+    #                0,  1, 2, 3, 4,  5,  6, 7
+    let lenToNum = [-1, -1, 1, 7, 4, -1, -1, 8]
+
+    var
+      decoded: array[10, Digit]
+      group235: seq[Digit]
+      group069: seq[Digit]
+
+    for digit in allDigits:
+      case len(digit):
+      of 2..4, 7:
+        decoded[lenToNum[len(digit)]] = digit
+      of 5:
+        group235.add(digit)
+      of 6:
+        group069.add(digit)
+      else: discard
+
+    for digit in group235:
+      if (digit - decoded[4]).len == 3:
+        decoded[2] = digit
+      elif (digit - decoded[1]).len == 3:
+        decoded[3] = digit
+      else:
+        decoded[5] = digit
+
+    for digit in group069:
+      if (digit - decoded[4]).len == 2:
+        decoded[9] = digit
+      elif (digit - decoded[7]).len == 4:
+        decoded[6] = digit
+      else:
+        decoded[0] = digit
+
+    for i, digit in decoded:
+      digitMap[cast[int](digit)] = i
+
+    var i = 0
+    # wish I could access the index in mapIt :/
+    let mapped = displayDigits.mapIt:
+      let power = 10^(3-i)
+      i += 1
+      digitMap[cast[int](it)] * power
+
+    sum += mapped.foldl(a+b)
+
+  echo "Sum of digits: ", sum
+
+main()