気負うことなくさっくりと.
tyama_henaf07.rb
#!/usr/bin/env ruby
#http://nabetani.sakura.ne.jp/hena/ordf07walk/
#https://qiita.com/Nabetani/items/cf93b63acc8a313c88bb
STDOUT.sync=true
while gets
a=$_.chomp.split('/').map{|e|e.chars.map(&:to_i)}
q=[[2,0]]
z={q[0]=>0}
while !q.empty?
cx,cy=q.shift
[[-1,0],[0,-1],[1,0],[0,1]].each{|dx,dy|
nx,ny=cx+dx,cy+dy
if 0<=nx&&nx<a[0].size && 0<=ny&&ny<a.size && !z[[nx,ny]] && (a[cy][cx]-a[ny][nx]).abs<=1
z[[nx,ny]]=z[[cx,cy]]+1
q<<[nx,ny]
end
}
a[cy][cx]='*'
end
puts a.map(&:join)*'/'
end