commit 0b0024ac521a4fa08090f939967b74b6d26c3539 · dunkirk.sh/aoc-2025

+129

nix/05/solution.nix

···

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       let

     

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         input = builtins.readFile ../../shared/05/input.txt;

     

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       +
         

     

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         # Split input into two sections

     

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         sections = builtins.filter (s: s != "") (builtins.split "\n\n" input);

     

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         rangesSection = builtins.head sections;

     

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         ingredientsSection = builtins.elemAt sections 2; # sections are [ranges, "\n\n", ingredients]

     

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       +
         

     

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         # Parse ranges from "start-end" format

     

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         rangeLines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" rangesSection);

     

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         parsedRanges = builtins.map (line:

     

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           let

     

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             parts = builtins.filter (s: builtins.isString s && s != "") (builtins.split "-" line);

     

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             start = builtins.fromJSON (builtins.head parts);

     

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             end = builtins.fromJSON (builtins.elemAt parts 1);

     

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           in { inherit start end; }

     

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         ) rangeLines;

     

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         # Sort ranges by start position using merge sort

     

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         sortedRanges = 

     

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           let

     

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             merge = left: right:

     

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               let

     

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                 mergeImpl = l: r: acc:

     

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                   if builtins.length l == 0 then acc ++ r

     

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                   else if builtins.length r == 0 then acc ++ l

     

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                   else

     

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                     let

     

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                       lHead = builtins.head l;

     

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                       rHead = builtins.head r;

     

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                       lTail = builtins.tail l;

     

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                       rTail = builtins.tail r;

     

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                     in if lHead.start <= rHead.start

     

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                        then mergeImpl lTail r (acc ++ [lHead])

     

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                        else mergeImpl l rTail (acc ++ [rHead]);

     

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               in mergeImpl left right [];

     

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       +
             

     

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             mergeSort = list:

     

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               let len = builtins.length list;

     

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               in if len <= 1 then list

     

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                  else

     

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                    let

     

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                      mid = len / 2;

     

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                      left = builtins.genList (i: builtins.elemAt list i) mid;

     

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                      right = builtins.genList (i: builtins.elemAt list (i + mid)) (len - mid);

     

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                    in merge (mergeSort left) (mergeSort right);

     

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           in mergeSort parsedRanges;

     

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         # Merge overlapping or adjacent ranges

     

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         mergedRanges = 

     

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           let

     

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             merge = builtins.foldl' (state: range:

     

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               if state.current == null then { current = range; result = []; }

     

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               else

     

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                 let curr = state.current;

     

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                 in if curr.end + 1 >= range.start then

     

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                   # Overlapping or adjacent - merge

     

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                   { current = { start = curr.start; end = if curr.end > range.end then curr.end else range.end; };

     

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                     result = state.result; }

     

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                 else

     

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                   # Gap - save current and start new

     

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                   { current = range;

     

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                     result = state.result ++ [curr]; }

     

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             ) { current = null; result = []; } sortedRanges;

     

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           in if merge.current == null then merge.result else merge.result ++ [merge.current];

     

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         # Parse ingredients

     

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         ingredientLines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" ingredientsSection);

     

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         ingredients = builtins.map (line: builtins.fromJSON line) ingredientLines;

     

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         # Sort ingredients using merge sort

     

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         sortedIngredients =

     

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           let

     

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             merge = left: right:

     

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               let

     

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                 mergeImpl = l: r: acc:

     

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                   if builtins.length l == 0 then acc ++ r

     

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                   else if builtins.length r == 0 then acc ++ l

     

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                   else

     

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                     let

     

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                       lHead = builtins.head l;

     

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                       rHead = builtins.head r;

     

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                       lTail = builtins.tail l;

     

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                       rTail = builtins.tail r;

     

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                     in if lHead <= rHead

     

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                        then mergeImpl lTail r (acc ++ [lHead])

     

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                        else mergeImpl l rTail (acc ++ [rHead]);

     

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               in mergeImpl left right [];

     

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             mergeSort = list:

     

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               let len = builtins.length list;

     

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               in if len <= 1 then list

     

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                  else

     

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                    let

     

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                      mid = len / 2;

     

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                      left = builtins.genList (i: builtins.elemAt list i) mid;

     

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                      right = builtins.genList (i: builtins.elemAt list (i + mid)) (len - mid);

     

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                    in merge (mergeSort left) (mergeSort right);

     

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           in mergeSort ingredients;

     

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         # Part 1: Count ingredients that fall within merged ranges

     

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         part1 =

     

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           let

     

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             # Use foldl' to process ingredients with range index tracking

     

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             result = builtins.foldl' (state: ingredient:

     

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               let

     

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                 # Find the appropriate range starting from current index

     

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                 findRange = rangeIdx:

     

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                   if rangeIdx >= builtins.length mergedRanges then { found = false; newIdx = rangeIdx; }

     

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                   else

     

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                     let range = builtins.elemAt mergedRanges rangeIdx;

     

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                     in if ingredient < range.start then { found = false; newIdx = rangeIdx; }

     

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                        else if ingredient <= range.end then { found = true; newIdx = rangeIdx; }

     

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                        else findRange (rangeIdx + 1);

     

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       +
                 

     

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                 rangeResult = findRange state.rangeIdx;

     

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               in {

     

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                 count = state.count + (if rangeResult.found then 1 else 0);

     

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                 rangeIdx = rangeResult.newIdx;

     

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               }

     

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             ) { count = 0; rangeIdx = 0; } sortedIngredients;

     

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           in result.count;

     

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         # Part 2: Total coverage of all merged ranges

     

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         part2 = builtins.foldl' (sum: range: sum + (range.end - range.start + 1)) 0 mergedRanges;

     

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       in {

     

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         inherit part1 part2;

     

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       }