Hello aspirant,
Yes, you can get admission to a Diploma in Computer Science after 12th in some colleges, especially private polytechnic institutes or in states that allow lateral or direct entry based on 12th marks. However, in most government polytechnic colleges, admission is usually based on entrance exams or 10th standard marks, not 12th. Some states may allow 12th science students (especially with PCM) to apply directly into the second year through lateral entry schemes.