CONCEPT · Novice
Contest I/O
also fast input · scanner
Problems specify a rigid input format. In a real contest you parse stdin exactly. In this MVP the arena calls a JavaScript function with parsed arguments instead.
Intuition
Wrong parsing is a WA that looks like a wrong algorithm. Read n, then exactly n tokens. Do not assume a trailing newline saves you.
When to reach for it
- Every Codeforces / AtCoder / USACO submission
- Multiple test cases (t up to 1e4 — empty the leftover state)
Usual pits
- Using slow C++ cin without ios::sync_with_stdio(false)
- Forgetting to reset arrays between test cases
- Printing extra debug lines