Solve day 1 part 1

.gitignore

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+day_*.txt
+

day_1.sml

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+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
+    (fn (line) =>
+        let val substr = Substring.extract (line, 0, NONE)
+        in [
+            substrToInt (Substring.takel Char.isDigit substr),
+            substrToInt (Substring.taker Char.isDigit substr)
+        ] end
+    )
+    lines
+
+val lists = (
+    sortAsc (map (fn (pair) => hd pair) pairs),
+    sortAsc (map (fn (pair) => List.last pair) pairs)
+)
+
+val distances = ListPair.map (fn (n1, n2) => abs(n1 - n2)) lists
+
+val totalDistance = sum distances
+