regular expression problem

i have this: ^(?!.*--)[A-Za-z\d-]+$ it accepts alphanumeric characters, optionally with single dash only and it does not accepts space. now i need it to accept space for example: ab34 12435, ab34- 12435 is valid. ab34 12435, ab34- 12435 is invalid. never mind the space before and end of the example.. i can trim that before i validate it to my problem regular expression
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