RosettaCodeData/Task/Run-length-encoding/Mathematica/run-length-encoding-1.math

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RunLengthEncode[input_String]:=StringJoin@@Sequence@@@({ToString @Length[#],First[#]}&/@Split[Characters[input]])
RunLengthDecode[input_String]:=StringJoin@@ConstantArray@@@Reverse/@Partition[(Characters[input]/.(ToString[#]->#&/@Range[0,9]))//.{x___,i_Integer,j_Integer,y___}:>{x,10i+j,y},2]