Solve day 2 part 2

day_1.sml

@@ -1,13 +1,13 @@
-val file = TextIO.openIn "day_1.txt";
+fun sortAsc (l: int list) : int list = ListMergeSort.sort (op >) l
+
+fun sum (l: int list) : int = foldl (op +) 0 l
+
+fun substrToInt (substr: substring) : int = valOf (Int.fromString (Substring.string substr))
+
+val file = TextIO.openIn "day_1.txt"
 val input = TextIO.inputAll file;
 TextIO.closeIn file;
 
-fun sortAsc (l: int list) : int list = ListMergeSort.sort (fn (a, b) => a > b) l
-
-fun sum (l: int list) : int = foldl (fn (a, b) => a + b) 0 l
-
-fun substrToInt(substr: substring) : int = valOf (Int.fromString (Substring.string substr))
-
 val lines = String.tokens (fn (char) => char = #"\n") input
 
 val pairs = map

day_2.sml

@@ -0,0 +1,41 @@
+fun deleteNth (l : int list, n : int) = List.take (l, n) @ List.drop (l, n + 1)
+
+fun isDecreasing (l : int list) =
+    ListPair.all (fn (a, b) => b < a andalso b >= a - 3) (l, tl l)
+
+fun isIncreasing (l : int list) =
+    ListPair.all (fn (a, b) => b > a andalso b <= a + 3) (l, tl l)
+
+fun withTolerance (f : (int list) -> bool) = fn (l : int list) =>
+    let val withRemoved = List.tabulate (List.length l, fn (i) => deleteNth (l, i))
+    in List.exists f withRemoved end
+
+val file = TextIO.openIn "day_2.txt"
+val input = TextIO.inputAll file;
+TextIO.closeIn file;
+
+val lines = String.tokens (fn (char) => char = #"\n") input
+
+val reports = map
+    (fn (line) =>
+        let val numbers = String.tokens Char.isSpace line
+        in map (fn (n) => valOf (Int.fromString n)) numbers end
+    )
+    lines
+
+(* Part 1 *)
+
+val safeReports = List.filter (fn (report) => isDecreasing report orelse isIncreasing report) reports
+
+val safeAmount = List.length safeReports
+
+(* Part 2 *)
+
+val toleratedReports = List.filter
+    (fn (report) =>
+        withTolerance isDecreasing report orelse withTolerance isIncreasing report
+    )
+    reports
+
+val toleratedAmount = List.length toleratedReports
+