ruby, 30 bytes

Result

AC

Duration

2147ms

Code [DL]

puts$_[/(.)\1 /?2:4]while gets

stdin

151 119
942 244
266 568
675 975
612 529
855 553
568 378
221 184
122 416
491 113
685 659
644 553
957 575
635 337
436 474
139 115
567 166
472 457
588 836
899 776
988 582
261 612
462 218
563 668
996 698
933 336
698 221
367 686
411 151
142 487
928 215
144 627

stdout

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

stderr

/volume/CODE:1: warning: regex literal in condition

strace

10    execve("/bin/sh", ["/bin/sh", "/root/script", "/volume/CODE"], 0x7ffe086a95f0 /* 9 vars */) = 0
12    execve("/usr/local/ruby-2.7.1/bin/ruby", ["/usr/local/ruby-2.7.1/bin/ruby", "/volume/CODE"], 0x56123c5add60 /* 9 vars */) = 0
11    execve("/bin/cat", ["cat", "-"], 0x56123c5add40 /* 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    +++ exited with 0 +++
10    --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12, si_uid=0, si_status=0, si_utime=6, si_stime=3} ---
10    +++ exited with 0 +++