21 lines
634 B
D
21 lines
634 B
D
import std.stdio, std.algorithm, std.typecons, std.range;
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auto hailstone(uint m) pure nothrow @nogc {
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return m
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.recurrence!q{ a[n - 1] & 1 ? a[n - 1] * 3 + 1 : a[n - 1]/2}
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.until!q{ a == 1 }(OpenRight.no);
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}
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void main() {
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enum M = 27;
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immutable h = M.hailstone.array;
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writeln("hailstone(", M, ")= ", h[0 .. 4], " ... " , h[$ - 4 .. $]);
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writeln("Length hailstone(", M, ")= ", h.length);
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enum N = 100_000;
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immutable p = iota(1, N)
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.map!(i => tuple(i.hailstone.walkLength, i))
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.reduce!max;
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writeln("Longest sequence in [1,", N, "]= ",p[1]," with len ",p[0]);
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}
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