As the previous answers state, it depends on your condo documents.
It's likely that the sidewalk itself is classified as either a "common element" or a "limited common element."
If it's a common element, then the condo association owns it and is responsible for maintaining it. And, unless your condo rules state differently (and they might), the association might also be responsible for snow shoveling and things like that.
If it's a limited common element, then the condo association still owns it. But there may be additional responsibilities assigned to you.
If you're in a townhouse, then it's possible that you own it. Again, check your condo documents. Or check the documents you received at settlement.
Hope that helps.