51 lines
1.4 KiB
D
51 lines
1.4 KiB
D
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import std.stdio;
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import std.array;
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import std.algorithm;
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import std.string;
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import std.conv;
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import std.math;
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struct Race {
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long time, dist;
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}
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Race[] parseRaces(string filename) {
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string[] lines = File(filename).byLineCopy.array;
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long[] times = lines[0].split(":")[1].strip.split.map!(to!long).array;
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long[] distances = lines[1].split(":")[1].strip.split.map!(to!long).array;
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Race[] result = new Race[](times.length);
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foreach (size_t i, long time; times) {
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result[i] = Race(time, distances[i]);
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}
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return result;
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}
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Race parseKernedRace(string filename) {
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string[] lines = File(filename).byLineCopy.array;
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long time = lines[0].split(":")[1].strip.split.join.to!long;
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long dist = lines[1].split(":")[1].strip.split.join.to!long;
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return Race(time, dist);
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}
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long computeSolutions(in Race r) {
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double D = r.time * r.time - 4 * r.dist;
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double t1 = (-r.time + sqrt(D)) / -2;
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double t2 = (-r.time - sqrt(D)) / -2;
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long minWinningTime = cast(long) (ceil(t1) == t1 ? t1 + 1 : ceil(t1));
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long maxWinningTime = cast(long) (floor(t2) == t2 ? t2 - 1 : floor(t2));
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return maxWinningTime - minWinningTime + 1;
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}
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void part1() {
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parseRaces("input.txt").map!computeSolutions.fold!((a, b) => a * b).writeln;
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}
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void part2() {
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parseKernedRace("input.txt").computeSolutions.writeln;
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}
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void main() {
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part1();
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part2();
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}
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