math.md

Math-ish primitives

Jngen provides several free functions and a generator class MathRandom to help generating numbers and combinatorial primitives. All interaction with MathRandom goes via its global instance called rndm. The source of randomness is rnd.

Standalone functions

bool isPrime(long long n)

• Returns: true if n is prime, false otherwise.
• Supported for all n from 1 to 3.8e18.
• Implemented with deterministic variation of the Miller-Rabin primality test so should work relatively fast (exact benchmark here).

MathRandom methods

long long randomPrime(long long n)

long long randomPrime(long long l, long long r)

• Returns: random prime in range [2, n) or [l, r] respectively.
• Throws if no prime is found on the interval.

long long nextPrime(long long n)

long long previousPrime(long long n)

• Returns: the first prime larger (or smaller) than n, including n.

Array partition(int n, int numParts, int minSize = 0, int maxSize = -1)

• Returns: a random ordered partition of n into numParts parts, where the size of each part is between minSize and maxSize. If maxSize is -1 (the default value) then sizes can be arbitrary large.

template<typename T>
TArray<TArray<T>> partition(TArray<T> elements, int numParts, int minSize = 0, int maxSize = -1)

• Returns: a random partition of the array elements into numParts parts.

template<typename T>
TArray<TArray<T>> partition(TArray<T> elements, const Array& sizes)

• Returns: a random partition of the array elements into parts, where the size of each part is specified.
• Note: sum(sizes) must be equal to elements.size().