How can I restore all files i deleted in the Applications floder? Actually, i just want to delete one file in the Application folder,but when i moved it to Trash, CleanMyMac notices me to use it to delete it clearly. 

However after i clicked yes, it deletes all items in the Application folder,including Office,i works and Adobe etc. 

I have re-installed the apps. But it seems the problem cannot be solved only by re-downloading the apps. 

Facetime cannot find the camera right now and there is no responses when i click the right bottom. 

Is there anyone can help me with this?
Without being at the helm of your computer, I would advise a fresh installation. Reboot into recovery mode and reinstall OS X. This should restore all system files, and your personal files should not be effected.

You can boot into recovery mode a number of ways. One would be to hold alt at boot, then select your Recovery HD. In some instances, an OS X user may not have this drive. Instead, you may want to try Command+Option+R for Internet recovery.

A program like PhotoRec, which comes bundled with TestDisk. http://www.cgsecurity.org/wiki/TestDisk_Download

It runs in Terminal, but you would be able to select your drive and recover all files. Note that any files that have been overwritten since they were deleted (which is very likely) will not be recoverable.