At university programming questions in algorithms and data structures classes usually give you an upper bound time complexity in Big-O notation to achieve full marks.
Programming questions on CodeForces, LeetCode and HackerRank don’t usually provide an upper bounds in Big-O notation but instead provide
- an input size of the type $$1 \leq n \leq 10^5$$
- and a time limit in seconds (usually 1 or 2 seconds).
It’s then up to you to find out what an appropriate run time for your algorithm would be. For example, you might get:
- 60% of the points for passing test cases in 2 seconds for input sizes $$1 \leq n \leq 10^3$$
- and 100% of the points for passing test cases in 2 seconds for input sizes $$1 \leq n \leq 10^5$$
How do I use this?
- check the input size in the problem statement e.g. $$1 \leq n \leq 10^5 = 100000$$
- check the table for the worst case runtime in big-O notation e.g. $$O(n\log_2n)$$
- chose your algorithm accordingly