maxn

In programming, maxn (often written as MAXN or maxN) is a conventional identifier used to denote the maximum size of a collection, such as the number of elements, nodes, or positions that a program must support. It is not a language feature; rather, it is a naming convention in source code, particularly in competitive programming templates.

Usage: In contest templates, maxn is defined as a compile-time constant to allocate static arrays or adjacency lists large enough to hold the largest possible input described in the problem statement. For example, in C++: const int MAXN = 100000; int a[MAXN+5];

Naming and alternatives: Variants include MAXN, NMAX, or maxN; some projects prefer more descriptive names such as LIMIT or CAP. In modern code, some use constexpr or templates instead of macros to avoid macro pitfalls.

Practical considerations: Choosing maxn too small causes out-of-bounds access; too large wastes memory. In languages with stack allocation, very large maxn can cause stack overflow; dynamic containers (vectors) can adjust to actual input size but may add overhead. In 1-based indexing, programmers often allocate maxn+5 to provide a safe margin.

Other uses: maxn can also appear in problem statements as a symbol representing the upper bound of n, the number of items in a set. It is commonly seen in tutorials, problem solutions, and CP libraries.