Regarding subtasks

could someone explain me about sub tasks

the problem consists of multiple subtasks ,
you get the point allocated for subtasks if your code passes the test files for that subtasks ,
the information about subtasks is provided in the problems .

All the problems are now partially graded and you will get score for passing certain test data which contains test files according to different TEST DATA CONTRAINTS. You receive hundred point for solving a problem if you pass all the subtasks and partial if you pass a subtask as a whole & not partially.

This type of scoring was used first time in November Long Challenge 2014 but it is used in all the LunchTime Contents which are hosted on every last Sunday of the month.