i:2!0:"i/23"
h:{(3(|/)':0,x,0)./:/:(0 1;0 -1)+\:/:y} / horizontal
c:4{+|(*&|/x)_'x}/                      / compress
step:{
 (j;b):x
 b:4(+|0,)/b                            / expand
 p:+&b
 m:(|'h[+b;|'p]),'|'h[b;p]
 n:{(2=#?x)*1+4!y+*&x@4!y+!4}[;j]'~m    / 0:/ 1:n 2:s 3:w 4:e
 v:,/.(1=#:')#=q:p+(0 0;-1 0;1 0;0 -1;0 1)n
 (1+j;c@b.[;;~:]/(p@v),q@v)}
+//~*|10 step/(0;i)
{(j;b):step@x;$[b~*|x;j;o(j;b)]}(0;i)