Struct Comb

pub struct Comb { /* private fields */ }

A struct for pre-calculating factorials and their modular inverses, useful for efficient combination and permutation calculations under mod.

Implementations

impl Comb

pub fn new(mod_value: u64, max_fact: usize) -> Comb

Creates a new Comb instance, pre-calculating factorials and their modular inverses up to max_fact.

This pre-computation allows for fast calculation of combinations and permutations modulo mod_value.

Arguments

• mod_value - The modulus to use for calculations.
• max_fact - The maximum number for which factorials and inverse factorials will be pre-calculated. This determines the range of n that can be used in nCr and nPr without requiring further calculations.

Panics

Panics if modulus is not prime.

pub fn nPr(&self, n: u64, r: u64) -> u64

Calculates nPr (n permutations of r) under mod.

Arguments

• n - The total number of items.
• r - The number of items to choose.

Panics

Panics if n is less than r or n > max_fact.

pub fn nCr(&self, n: u64, r: u64) -> u64

Calculates nCr (n combinations of r) under mod.

Arguments

• n - The total number of items.
• r - The number of items to choose.

Panics

Panics if n is less than r or n > max_fact.