53 lines
1.3 KiB
D
53 lines
1.3 KiB
D
import std;
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alias Unit = void[0];
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alias Set(T) = Unit[T];
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auto toSet(R)(R r)
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{
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return r.map!(element => tuple(element, Unit.init)).assocArray;
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}
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auto setOf(T)(T[] elements...)
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{
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return elements.toSet;
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}
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void main()
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{
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auto nodes = File("input", "r").byLine.map!(to!int).chain([0]).toSet;
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nodes.calculateNumberOfPathsLeadingFromTo(0, nodes.byKey.maxElement).writeln;
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}
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ulong calculateNumberOfPathsLeadingFromTo(Set!int nodes, int start, int end)
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{
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if (end == start)
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{
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return 1;
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}
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return iota(end - 3, end).filter!(potentialAncestor => potentialAncestor in nodes)
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.map!(ancestor => nodes.memoize!calculateNumberOfPathsLeadingFromTo(start, ancestor))
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.sum;
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}
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unittest
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{
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Set!int input = setOf(0, 1);
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assert(input.calculateNumberOfPathsLeadingFromTo(0, 1) == 1);
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}
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unittest
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{
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auto input = [16, 10, 15, 5, 1, 11, 7, 19, 6, 12, 4].chain([0]).toSet;
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assert(input.calculateNumberOfPathsLeadingFromTo(0, input.byKey.maxElement) == 8);
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}
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unittest
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{
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auto input = [
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28, 33, 18, 42, 31, 14, 46, 20, 48, 47, 24, 23, 49, 45, 19, 38, 39, 11,
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1, 32, 25, 35, 8, 17, 7, 9, 4, 2, 34, 10, 3
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].chain([0]).toSet;
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assert(input.calculateNumberOfPathsLeadingFromTo(0, input.byKey.maxElement) == 19_208);
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}
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