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1-liner: 121 solution in Creative category for Reverse Roman Numerals by przemyslaw.daniel
reverse_roman=lambda n,f='IVXLCDM'.index:sum((1,5)[f(i)%2]*10**(f(i)//2)*(-1,1)[f(i)>=f(j)]for i,j in zip(n,n[1:]+n[-1]))
July 31, 2017