Sync pictures deleted apps

I connected my iPhone4 to my PC to sync pictures. Worked great.

Problem: after syncing, I realized several apps were deleted from my iPhone. These are apps that I paid for, not free ones, or I would have just downloaded them again.

I have synced this phone to a different PC laptop also. So the apps were stored on that harddrive. I copied the apps over to the PC which I used to sync the pictures, so that the apps would be transferred to the phone again, but then those apps were deleted from the PC!

How do I get my apps back?