185 - with an unusual use of $PIECE instead of $SELECT to save 2 characters, which would also shorten yours to 184

1 s c=",",x=$p(a,c,$i(i)) q:x="" o f{s y=$p(a,c,$i(j)+i),g=$g(g,y-x) q:j*g+x'=y  s l="-"_y} s g=$zabs(g),$p(o,c,$i(p))=x s:2-'g<j o=o_$s(g:l_$p("/"_g,c,g>1),1:"*"_j),i=i+j-1 k g,j g 1

f i=1:1:2e6{s x=",",a=$p(s,x,i),d=$p(s,x,i+1)-a f c=1:1{q:d*c+a'=$p(s,x,i+c)} s q=$zabs(d),v=$s(c>2&d:"-"_(c-1*d+a)_$p("/"_q,x,q>1),c>1&'d:"*"_c,1:0) s:v'=0 $p(s,x,i,i+c-1)=a_v} q s

Hi Vitaliy,

Out of curiosity I had a go at this. I can't get under 188 using my own ideas and code:

1 s c=",",x=$p(a,c,$i(i)) q:x="" o f{s y=$p(a,c,$i(j)+i),g=$g(g,y-x) q:j*g+x'=y  s l=y} s g=$zabs(g),$p(o,c,$i(p))=x s:2-'g<j o=o_$s(g:"-"_l_$s(g>1:"/"_g,1:""),1:"*"_j),i=i+j-1k g,j g 1

You could shave 2 characters off each of your versions by having a variable contain the comma:

a s x=",",a=$p(s,x,$i(i)),d=$p(s,x,i+1)-a f c=1:1{q:d*c+a'=$p(s,x,i+c)} s q=$zabs(d),v=$s(c>2&d:"-"_(c-1*d+a)_$s(q=1:"",1:"/"_q),c>1&'d:"*"_c,1:0) s:v'=0 $p(s,x,i,i+c-1)=a_v q:a="" s g a

Ah, you are correct. My test cases for a fail were of differing lengths. Doh!

What is needed is a simple command to sort the letters into a consistent order before comparison.