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import std.stdio, std.algorithm, std.math;
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double entropy(T)(T[] s)
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pure nothrow if (__traits(compiles, s.sort())) {
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immutable sLen = s.length;
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return s
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.sort()
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.group
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.map!(g => g[1] / double(sLen))
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.map!(p => -p * p.log2)
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.sum;
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}
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void main() {
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"1223334444"d.dup.entropy.writeln;
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}
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