perl, 28 bytes

Result

AC

Duration

604ms

Code [DL]

print<>=~s/(.)(\d)/$1x$2/gre

stdin

o4o5g5v4s5n6u7hcc2x6o9f5q6w5l5s9y9e9w4i3rk7k5p7e2v9h2z7p6y5kadsj8c8w7s7q5pk3c2m7b4b3p9p6t4c6

stdout

ooooooooogggggvvvvsssssnnnnnnuuuuuuuhcccxxxxxxooooooooofffffqqqqqqwwwwwlllllsssssssssyyyyyyyyyeeeeeeeeewwwwiiirkkkkkkkkkkkkpppppppeevvvvvvvvvhhzzzzzzzppppppyyyyykadsjjjjjjjjccccccccwwwwwwwsssssssqqqqqpkkkccmmmmmmmbbbbbbbpppppppppppppppttttcccccc

stderr

strace