105 106 107 108 109 110 111 112 113
1115 1116 1117 1118 1119 1120 1121 1122 1123
12345 12346 12347 12348 12349 12350 12351 12353

##</code><code>##

105 106 107 108 109
110 111 112 113
1115 1116 1117 1118 1119 
1120 1121 1122 1123
12345 12346 12347 12348 12349 
12350 12351 12353

##</code><code>##

#! perl -slw
use strict;

while( <DATA> ) {
    s[\s(\d+)\d\d\K\s(?=(\d+)\d\d\s)]{
        $1 + 1 == $2 ? "\n" : ' '
    }ge;
    print;
}

__DATA__
105 106 107 108 109 110 111 112 113
1115 1116 1117 1118 1119 1120 1121 1122 1123
12345 12346 12347 12348 12349 12350 12351 12353

##</code><code>##

perl -ple"s[(?<=\s(\d{3})\d\d)\s(?=(\d{3})\d\d\s)][$1+1==$2 ? qq[\n] : ' ' ]ge" in > out