For the very last slot, Wasif leaves it open: design and fully write your own original problem statement combining at least three ideas from this entire practice sheet, in true contest-author style, and then solve it yourself within 45 minutes. Design and solve a single problem of your own that combines at least THREE ideas from this practice sheet (e.g., binary search on the answer + prefix sums + number theory, or graph BFS + greedy + DP). Write the full problem statement (context, input, output, constraints, sample) yourself, then solve it in C within 45 minutes. This exercise trains the hardest and most important contest skill: reading/creating a problem's structure under time pressure, not just coding a known pattern.
Input
Output
Open-ended problem — design your own statement, then use Run with custom input. Auto-submit is disabled.
Write C, then Run (custom I/O) or Submit (sample tests). ⌘/Ctrl+Enter submits.