Problems are organized based on the components in their name. A typical problem will look like:
abc123_a
The problem is made up of three components: abc 123 and a.
abc stands for "AtCoder Basic Contest" which is the first of three competitor levels. The other two are arc (AtCoder Regular Contest) and agc (AtCoder Grand Contest), each more difficult than the previous.
123 represents the contest number under the contest's respective category. In this case, 123 would mean the 123rd contest to take place.
a represents the task within the contest. In general, contests contain between four to seven increasingly difficult problems labeled a to f2.
Tasks are also grouped based on overall difficulty. For example, task a and task b may fall within the same difficulty gradient for a given contest despite task b being more challenging on average.
The categories in order of difficulty from easiest to hardest are:
- Gray
- Brown
- Green
- Cyan
- Blue
- Yellow
- Orange
- Red