commit a57df37e3d99dfc5f4a0c14ee0ee61e2cf779e75 · dunkirk.sh/aoc-2025

+76

nix/02/solution.nix

···

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       let

     

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         input = builtins.readFile ../../shared/02/input.txt;

     

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         # Parse comma-separated ranges into list of {start, end}

     

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         ranges = 

     

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           let

     

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             rangeStrings = builtins.filter builtins.isString (builtins.split "," input);

     

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             parseRange = str:

     

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               let parts = builtins.match "([0-9]+)-([0-9]+)" str;

     

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               in { start = builtins.fromJSON (builtins.elemAt parts 0); 

     

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

     

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           in map parseRange rangeStrings;

     

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         # Convert number to string digits

     

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         numToStr = n: builtins.toString n;

     

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         # Check if string has even length and halves are equal

     

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         hasEqualHalves = str:

     

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           let len = builtins.stringLength str;

     

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               half = len / 2;

     

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           in if len == 0 || (len / 2 * 2) != len then false

     

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              else (builtins.substring 0 half str) == (builtins.substring half half str);

     

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         # Check if string is repeating pattern of given chunk size

     

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         isRepeating = str: chunkSize:

     

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           let 

     

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             len = builtins.stringLength str;

     

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             chunk = builtins.substring 0 chunkSize str;

     

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             checkPos = pos: 

     

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               if pos >= len then true

     

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               else if (builtins.substring pos chunkSize str) != chunk then false

     

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               else checkPos (pos + chunkSize);

     

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           in if len == 0 || (len / chunkSize * chunkSize) != len then false

     

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              else checkPos 0;

     

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         # Find smallest repeating chunk size for a string

     

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         hasRepeatingPattern = str:

     

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           let 

     

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             len = builtins.stringLength str;

     

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             checkSize = size:

     

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               if size > len / 2 then false

     

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               else if isRepeating str size then true

     

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               else checkSize (size + 1);

     

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           in if len == 0 then false else checkSize 1;

     

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         # Process range in batches to avoid stack overflow

     

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         sumRangeIf = predicate: start: end:

     

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           let

     

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             batchSize = 10000;

     

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             numBatches = ((end - start + 1) + batchSize - 1) / batchSize;

     

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             processBatch = i:

     

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               let

     

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                 batchStart = start + i * batchSize;

     

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                 batchEnd = if batchStart + batchSize - 1 < end then batchStart + batchSize - 1 else end;

     

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                 nums = builtins.genList (n: batchStart + n) (batchEnd - batchStart + 1);

     

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                 validNums = builtins.filter predicate nums;

     

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               in builtins.foldl' (a: n: a + n) 0 validNums;

     

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           in builtins.foldl' (acc: i: acc + processBatch i) 0 (builtins.genList (i: i) numBatches);

     

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         part1 =

     

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           let

     

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             processRange = acc: r:

     

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               acc + sumRangeIf (n: hasEqualHalves (numToStr n)) r.start r.end;

     

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           in builtins.foldl' processRange 0 ranges;

     

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         part2 =

     

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           let

     

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             processRange = acc: r:

     

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               acc + sumRangeIf (n: hasRepeatingPattern (numToStr n)) r.start r.end;

     

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           in builtins.foldl' processRange 0 ranges;

     

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       in {

     

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         inherit part1 part2;

     

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       }