bash-pure, 87 bytes

Result

WA

Code [DL]

while read -n 1 c;do a[c]=${a[c]}@;done
for i in {0..9};do echo -n ${a[c]//@/$i}$i;done

stdin

9452310148041237046549274444119292684411920217375149852638729962377851925654644286166258879946461751

stdout

00000111112222233333444445555566666777778888899999

stderr

/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

strace