vim, 29 bytes

Result

WA

Duration

803ms

Code [DL]

:%s/.*\(.\)\(\1\| \).*/\1/
ZZ

Disassembly

:%s/.*\(.\)\(\1\| \).*/\1/<NL>ZZ

stdin

921 377
848 843
535 554
614 651
744 441
977 441
342 826
271 159
433 712
216 518
488 441
752 271
753 762
199 194
344 441
465 671
188 284
858 993
245 842
518 187
892 529
533 372
521 377
433 523
332 383
763 883
589 996
952 551
755 511
845 548
557 556
893 937

stdout

7
8
5
4
4
4
2
1
3
6
4
2
3
9
4
5
8
9
5
8
2
3
7
3
2
8
9
5
1
5
5
3

stderr

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffc813e4b40 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x560d9b89fd00 /* 9 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/vim", ["/usr/bin/vim", "-N", "-u", "NONE", "-i", "NONE", "-s", "/volume/CODE", "/tmp/out"], 0x560d9d065288 /* 10 vars */) = 0
12    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
13    execve("/bin/cat", ["cat", "/tmp/out"], 0x560d9b89fc98 /* 9 vars */) = 0
13    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=13, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
14    execve("/bin/rm", ["rm", "/tmp/out"], 0x560d9b89fc98 /* 9 vars */) = 0
14    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
10    +++ exited with 0 +++