ocaml, 128 bytes

Result

AC

Duration

707ms

Code [DL]

let rec f?(c=input_char stdin)x=let x=(match c with 'T'->0|'K'->x-50|_->x+1)mod 51 in
print_char(if x<1 then 'x'else c);f x;;f 0

stdin

                T                                 
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
        K                                         

stdout

                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
                x                                 
        xxxxxxxxx                                 

stderr

Exception: End_of_file.

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffe7350e580 /* 7 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x555a022c3d30 /* 7 vars */) = 0
11    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
12    execve("/usr/bin/ocaml", ["/usr/bin/ocaml", "/volume/CODE"], 0x555a022c3d40 /* 7 vars */) = 0
12    +++ exited with 2 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=2, si_utime=2, si_stime=0} ---
10    +++ exited with 2 +++