36 lines
898 B
Java
36 lines
898 B
Java
package Maths;
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/** @see <a href="https://en.wikipedia.org/wiki/Combination">Combination</a> */
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public class Combinations {
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public static void main(String[] args) {
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assert combinations(1, 1) == 1;
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assert combinations(10, 5) == 252;
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assert combinations(6, 3) == 20;
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assert combinations(20, 5) == 15504;
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}
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/**
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* Calculate of factorial
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*
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* @param n the number
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* @return factorial of given number
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*/
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public static long factorial(int n) {
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if (n < 0) {
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throw new IllegalArgumentException("number is negative");
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}
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return n == 0 || n == 1 ? 1 : n * factorial(n - 1);
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}
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/**
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* Calculate combinations
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*
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* @param n first number
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* @param k second number
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* @return combinations of given {@code n} and {@code k}
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*/
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public static long combinations(int n, int k) {
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return factorial(n) / (factorial(k) * factorial(n - k));
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}
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}
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