Add the mathematical operators + or - before any of the digits in the decimal numeric string 123456789 such that the resulting mathematical expression adds up to 100. Return all possible solutions.

There are 12 solutions:

1+2+3-4+5+6+78+9
1+2+34-5+67-8+9
1+23-4+5+6+78-9
1+23-4+56+7+8+9
12+3+4+5-6-7+89
12+3-4+5+67+8+9
12-3-4+5-6+7+89
123+4-5+67-89
123+45-67+8-9
123-4-5-6-7+8-9
123-45-67+89
-1+2-3+4+5+6+78+9