Day 04

day04/default.nix

@@ -0,0 +1,46 @@
+{ pkgs, lib }:
+
+with lib;
+
+let
+  sections = pipe (fileContents ./input.txt) [
+    (splitString "\n")
+    (map (splitString ","))
+    (map (map toElfRange))
+    (map (x: {
+      e1 = elemAt x 0;
+      e2 = elemAt x 1;
+    }))
+  ];
+
+  toElfRange = start-end:
+    let splitSE = splitString "-" start-end;
+    in {
+      start = toInt (elemAt splitSE 0);
+      end = toInt (elemAt splitSE 1);
+    };
+  
+  eitherContainsTheOther = { e1, e2 }:
+       ((e2.start <= e1.start) && (e1.end <= e2.end))
+    || ((e1.start <= e2.start) && (e2.end <= e1.end));
+
+  answer1 = pipe sections [
+    (count eitherContainsTheOther)
+    toString
+  ];
+
+  eitherOverlapsTheOther = { e1, e2 }:
+    e1.start <= e2.end && e2.start <= e1.end;
+
+  answer2 = pipe sections [
+    (count eitherOverlapsTheOther)
+    toString
+  ];
+
+in pkgs.writeText "answers" ''
+  Task1:
+    ${answer1}
+
+  Task2:
+    ${answer2}
+''

flake.nix

@@ -6,9 +6,10 @@
     pkgs = nixpkgs.legacyPackages.${system};
   in {
     packages.${system} = {
-      day01 = pkgs.callPackage ./day01 {};
-      day02 = pkgs.callPackage ./day02 {};
-      day03 = pkgs.callPackage ./day03 {};
+      day01 = pkgs.callPackage ./day01 { };
+      day02 = pkgs.callPackage ./day02 { };
+      day03 = pkgs.callPackage ./day03 { };
+      day04 = pkgs.callPackage ./day04 { };
     };
   };
 }