solution 2

solutions/day02/example.txt

@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9

solutions/day02/solution.nim

@@ -0,0 +1,64 @@
+import std/[strutils, algorithm, sequtils]
+import aoc
+
+proc parseInput(input: string): seq[seq[int]] =
+  for line in input.splitLines():
+    result.add line.splitWhitespace().mapIt(parseInt(it))
+
+proc checkPair(x, y: int): bool =
+  if y < x: return false
+  let dist = abs(y - x)
+  if dist < 1 or dist > 3: return false
+  return true
+
+proc checkWindow(x, y, z: int): bool =
+  if not [x, y, z].isSorted: return false
+  let dists = [abs(z-y), abs(y-x)]
+  if dists.filterIt(it < 1 or it > 3).len != 0: return false
+  return true
+
+proc isSafe(report: seq[int]): bool =
+  var levels = report
+  # make all lists ascending order
+  if levels[0] > levels[1]:
+    levels.reverse()
+  for i in 0..<levels.len:
+    if i == 0:
+      if not checkPair(levels[i], levels[i + 1]):
+        return false
+    elif i == levels.len - 1:
+      if not checkPair(levels[i - 1], levels[i]):
+        return false
+    else:
+      if not checkWindow(levels[i - 1], levels[i], levels[i+1]):
+        return false
+  result = true
+
+
+proc partOne*(input: string): int =
+  parseInput(input).filterIt(it.isSafe()).len
+
+proc leaveOneOutCheck(report: seq[int]): bool =
+  let leaveOneOutReports =
+    @[report[1..^1]] & (1..<report.len).mapIt(report[0 .. it - 1] & report[it + 1 .. ^1])
+
+  for report in leaveOneOutReports:
+    if isSafe report:
+      return true
+
+proc partTwo*(input: string): int =
+  ## brutest of force
+  for report in parseInput(input):
+    if isSafe report:
+      inc result
+    else:
+      if leaveOneOutCheck report:
+        inc result
+
+solve:
+  "example.txt":
+    partOne: 2
+    partTwo: 4
+  "input.txt":
+    partOne: 624
+    partTwo: 658