diff --git a/2021/common.nim b/2021/common.nim
index 510053a..052f581 100644
--- a/2021/common.nim
+++ b/2021/common.nim
@@ -1,4 +1,4 @@
-import std/[streams, sequtils, strutils, sugar, strformat, times, httpclient, os]
+import std/[streams, sequtils, strutils, sugar, strformat, times, httpclient, os, options]
 
 const YEAR = getEnv("AOC_YEAR", "2021").parseInt()
 proc getCookie(): string = "~/.advent-of-code-auth-cookie".expandTilde().readFile()
@@ -35,3 +35,19 @@ template time*(i: string, body: untyped): untyped =
   when not defined(release):
     echo "NOTE: This is not a real measurement of performance. Compile in release mode with -d:release for best performance."
   # jkp: {(stop - start) * 1000} ms to calculate solution: {result}"
+
+proc doDay*[T](
+  day: int,
+  inputLoader: int -> T,
+  part1: T -> int,
+  part2: T -> int,
+  testInput: T,
+  expectedPart1: int,
+  expectedPart2: int): void =
+  let input = day.inputLoader()
+  time(&"day {day} part 1"): echo input.part1()
+  time(&"day {day} part 2"): echo input.part2()
+
+  when not defined(release):
+    doAssert testInput.part1() == expectedPart1
+    doAssert testInput.part2() == expectedPart2
diff --git a/2021/seven.nim b/2021/seven.nim
index cb11319..1b27b0e 100644
--- a/2021/seven.nim
+++ b/2021/seven.nim
@@ -1,33 +1,18 @@
-import std/[strutils, sequtils, tables, strformat]
+import std/[strutils, sequtils, strformat]
 import ./common
 
-proc crabsDistance(input: string): int =
+proc crabFuel(input: string): int =
+  let crabs = input.split(',').map(parseInt)
   result = int.high()
-  var max_try = 0
-  let dists = input.split(',').map(parseInt)
-  for d in dists:
-    if d > max_try: max_try = d
-  for t in 0..max_try:
-    let fuel = dists.foldl(a + abs(b - t), 0)
-    if fuel < result: result = fuel
+  var maxCrab = crabs.foldl(max(a, b), 0)
+  for t in 0..maxCrab: result = min(crabs.foldl(a + abs(b - t), 0), result)
 
-proc f(n: int): int = toSeq(0..abs(n)).foldl(a + b, 0)
+proc triangleNumber(n: int): int = int((n * (n + 1)) / 2)
 
-proc crabsBigDistance(input: string): int =
+proc crabMoreFuel(input: string): int =
+  let crabs = input.split(',').map(parseInt)
   result = int.high()
-  var max_try = 0
-  let dists = input.split(',').map(parseInt)
-  for d in dists:
-    if d > max_try: max_try = d
-  for t in 0..max_try:
-    let fuel = dists.foldl(a + f(b - t), 0)
-    if fuel < result: result = fuel
+  var maxCrab = crabs.foldl(max(a, b), 0)
+  for t in 0..maxCrab: result = min(crabs.foldl(a + (b - t).abs().triangleNumber(), 0), result)
 
-let input = 7.loadInputText()
-time("day 7 part 1"): echo input.crabsDistance()
-time("day 7 part 2"): echo input.crabsBigDistance()
-
-when not defined(release):
-  let testInput = "16,1,2,0,4,2,7,1,2,14"
-  doAssert testInput.crabsDistance() == 37
-  doAssert testInput.crabsBigDistance() == 168
+doDay(7, loadInputText, crabFuel, crabMoreFuel, "16,1,2,0,4,2,7,1,2,14", 37, 168)