The User Guide for Math Combinator Framework in Java Class Libraries)
Guide to use the mathematical combination framework in Java Library
When developing Java applications, mathematical combinations are often encountered.To simplify this operation, the Java class library provides a mathematical combination framework, making the processing combination problem easier and efficient.This article will introduce how to use the mathematical combination framework in the Java library and provide some Java code examples.
1. Introduce mathematical combination framework
First, the mathematical combination framework library is introduced in the Java project.You can use Maven or Gradle and other construction tools to manage project dependencies and add the following dependencies:
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-math3</artifactId>
<version>3.6.1</version>
</dependency>
2. Combination calculation function
The mathematical combination framework in the Java class library provides a variety of combined calculation functions to meet different needs.Here are some commonly used combined calculation functions and its usage:
-Acrusion quantity calculation
Use the `Combinatoricsutils.binomialCoefficient (int n, int K)` function can calculate the number of combinations of K element from n elements.
import org.apache.commons.math3.util.CombinatoricsUtils;
public class CombinationsDemo {
public static void main(String[] args) {
int n = 5; // Total element
int k = 3; // The number of elements selected
long combinations = CombinatoricsUtils.binomialCoefficient(n, k);
System.out.println ("Select the" + K + "element number of" + K + "elements from" + N + "is:" + Combinings);
}
}
Output results:
The number of combinations of 3 elements from 5 elements is: 10
-Colon the combination list
Use the `CombinatoricsUtils.combinationSitrator (int n, int k) function to get all combinations of selecting K elements from N elements.
import org.apache.commons.math3.util.CombinatoricsUtils;
import org.apache.commons.math3.util.Combinations;
public class CombinationsDemo {
public static void main(String[] args) {
int n = 5; // Total element
int k = 3; // The number of elements selected
Combinations combinations = new Combinations(n, k);
for (int[] combination : combinations) {
System.out.println(Arrays.toString(combination));
}
}
}
Output results:
[0, 1, 2]
[0, 1, 3]
[0, 1, 4]
[0, 2, 3]
[0, 2, 4]
[0, 3, 4]
[1, 2, 3]
[1, 2, 4]
[1, 3, 4]
[2, 3, 4]
-Che other combination calculation function
In addition to the above functions, there are some other useful combination calculation functions.For example:
-` CombinatoricsUtils.Factorial (int N) `: Calculate the step of n.
-` CombinatoricsUtils.stirlings2 (int n, int k) `: Calculate the second type of Stirling.
-` Combinatoricsutils.bell (int n) `: Calculate the number of bell.
3. Example: Select from a set of elements and print the possible combinations
The following is a complete example. Demonstration of how to use the mathematical combination framework to select and print the possible combinations of the possible combinations.
import org.apache.commons.math3.util.Combinations;
import java.util.Arrays;
public class CombinationsDemo {
public static void main(String[] args) {
int[] elements = {1, 2, 3, 4};
int k = 2; // The number of elements selected
Combinations combinations = new Combinations(elements.length, k);
for (int[] combination : combinations) {
int[] selectedElements = new int[k];
for (int i = 0; i < k; i++) {
selectedElements[i] = elements[combination[i]];
}
System.out.println(Arrays.toString(selectedElements));
}
}
}
Output results:
[1, 2]
[1, 3]
[1, 4]
[2, 3]
[2, 4]
[3, 4]
The above is the guidelines for the use of the mathematical combination framework in the Java class library.By using this framework, we can easily handle mathematical combination calculation problems to improve our development efficiency.
I hope this article can help you understand and use the mathematical combination framework in the Java library.
