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https://github.com/HenkKalkwater/aoc-2020
synced 2024-11-22 11:05:18 +00:00
Brute forcing does not work
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@ -7,8 +7,9 @@ struct ParsedInput {
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Variant run(int part, File input, bool bigboy, string[] args) {
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ParsedInput pInput = input.byLineCopy.array.parseInput();
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Variant result = parts!int(part,
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() => part1(pInput));
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Variant result = parts!long(part,
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() => part1(pInput),
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() => part2(pInput, 100000000000000));
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return result;
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}
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@ -17,17 +18,15 @@ Variant run(int part, File input, bool bigboy, string[] args) {
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ParsedInput input;
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input.timestamp = to!int(range[0]);
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input.busses = range[1].splitter(',').filter!(c => c != "x").map!(to!int).array;
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input.busses = range[1].splitter(',').map!(c => c == "x" ? -1 : c.to!int).array;
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writeln(input);
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return input;
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}
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int part1(ParsedInput input) {
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import std.math;
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int earliestBus = 0;
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int earliestBusTimestamp = int.max;
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foreach(int bus; input.busses) {
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foreach(int bus; input.busses.filter!(x => x != -1)) {
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int closestTimestamp = (input.timestamp / bus + 1 ) * bus;
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writeln(closestTimestamp);
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if (closestTimestamp < earliestBusTimestamp) {
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@ -35,10 +34,45 @@ int part1(ParsedInput input) {
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earliestBus = bus;
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}
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}
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writefln("Bus %d at %d", earliestBus, earliestBusTimestamp);
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// debug writefln("Bus %d at %d", earliestBus, earliestBusTimestamp);
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return earliestBus * (earliestBusTimestamp - input.timestamp);
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}
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long part2(ParsedInput input) {
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long result = 0;
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long startI = startFrom == 0 ? 0 : startFrom / input.busses[0];
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for (long i = startI; result == 0; i++) {
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long offset = i * input.busses[0];
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bool fail = false;
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foreach(j, subsequentBus; input.busses[1..$].enumerate(1)) {
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if (subsequentBus == -1) continue;
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if ((offset + j) % subsequentBus != 0) {
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fail = true;
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break;
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}
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}
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if (!fail) {
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result = offset;
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}
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debug {
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if (i % 10000 == 0) {
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writef("\rAt %d", offset);
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stdout.flush();
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}
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}
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}
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debug writeln();
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return result;
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}
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unittest {
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string[] input = [
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"939",
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@ -48,4 +82,5 @@ unittest {
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ParsedInput pInput = parseInput(input);
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assert(part1(pInput) == 295);
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assert(part2(pInput) == 1068781);
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}
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