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refactor: Enhance docs, code, add tests in `LinearDiophantineEquation… (#6744)
refactor: Enhance docs, code, add tests in `LinearDiophantineEquationsSolver`
This commit is contained in:
Hardik Pawar
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package com.thealgorithms.maths;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import org.junit.jupiter.api.Test;
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/**
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* Test class for LinearDiophantineEquationsSolver.
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* Tests various cases including:
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* - Equations with solutions
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* - Equations with no solutions
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* - Special cases (zero coefficients, infinite solutions)
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* - Edge cases (negative coefficients, large numbers)
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*/
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class LinearDiophantineEquationsSolverTest {
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/**
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* Tests the example equation 3x + 4y = 7.
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* Expected solution: x = -9, y = 8 (or other valid solutions).
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*/
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@Test
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void testBasicEquation() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(3, 4, 7);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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// Verify that the solution satisfies the equation
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with no solution: 2x + 4y = 5.
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* Since gcd(2, 4) = 2 and 2 does not divide 5, no solution exists.
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*/
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@Test
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void testNoSolution() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(2, 4, 5);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertEquals(LinearDiophantineEquationsSolver.Solution.NO_SOLUTION, solution);
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}
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/**
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* Tests the trivial equation 0x + 0y = 0.
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* This has infinite solutions.
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*/
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@Test
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void testInfiniteSolutions() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(0, 0, 0);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertEquals(LinearDiophantineEquationsSolver.Solution.INFINITE_SOLUTIONS, solution);
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}
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/**
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* Tests an equation where a = 0: 0x + 5y = 10.
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* Expected solution: x = 0, y = 2.
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*/
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@Test
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void testZeroCoefficient() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(0, 5, 10);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation where b = 0: 3x + 0y = 9.
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* Expected solution: x = 3, y can be anything (solver will return y = 0).
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*/
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@Test
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void testZeroCoefficientB() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(3, 0, 9);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with negative coefficients: -3x + 4y = 7.
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*/
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@Test
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void testNegativeCoefficients() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(-3, 4, 7);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with negative result: 3x + 4y = -7.
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*/
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@Test
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void testNegativeResult() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(3, 4, -7);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with coprime coefficients: 7x + 11y = 1.
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* Since gcd(7, 11) = 1, a solution exists.
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*/
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@Test
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void testCoprimeCoefficients() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(7, 11, 1);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with larger coefficients: 12x + 18y = 30.
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* Since gcd(12, 18) = 6 and 6 divides 30, a solution exists.
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*/
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@Test
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void testLargerCoefficients() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(12, 18, 30);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation that has no solution due to GCD: 6x + 9y = 5.
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* Since gcd(6, 9) = 3 and 3 does not divide 5, no solution exists.
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*/
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@Test
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void testNoSolutionGcdCheck() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(6, 9, 5);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertEquals(LinearDiophantineEquationsSolver.Solution.NO_SOLUTION, solution);
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}
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/**
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* Tests the equation x + y = 1.
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* Simple case where gcd(1, 1) = 1.
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*/
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@Test
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void testSimpleCase() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(1, 1, 1);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests Solution equality.
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*/
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@Test
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void testSolutionEquality() {
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final var solution1 = new LinearDiophantineEquationsSolver.Solution(3, 5);
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final var solution2 = new LinearDiophantineEquationsSolver.Solution(3, 5);
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final var solution3 = new LinearDiophantineEquationsSolver.Solution(3, 6);
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assertEquals(solution1, solution2);
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assertNotEquals(solution3, solution1);
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assertEquals(solution1, solution1);
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assertNotEquals(null, solution1);
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assertNotEquals("string", solution1);
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}
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/**
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* Tests Solution hashCode.
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*/
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@Test
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void testSolutionHashCode() {
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final var solution1 = new LinearDiophantineEquationsSolver.Solution(3, 5);
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final var solution2 = new LinearDiophantineEquationsSolver.Solution(3, 5);
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assertEquals(solution1.hashCode(), solution2.hashCode());
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}
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/**
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* Tests Solution toString.
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*/
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@Test
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void testSolutionToString() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(3, 5);
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final var str = solution.toString();
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assertTrue(str.contains("3"));
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assertTrue(str.contains("5"));
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assertTrue(str.contains("Solution"));
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}
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/**
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* Tests GcdSolutionWrapper equality.
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*/
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@Test
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void testGcdSolutionWrapperEquality() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(1, 2);
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final var wrapper1 = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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final var wrapper2 = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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final var wrapper3 = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(6, solution);
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assertEquals(wrapper1, wrapper2);
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assertNotEquals(wrapper3, wrapper1);
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assertEquals(wrapper1, wrapper1);
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assertNotEquals(null, wrapper1);
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assertNotEquals("string", wrapper1);
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}
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/**
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* Tests GcdSolutionWrapper hashCode.
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*/
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@Test
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void testGcdSolutionWrapperHashCode() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(1, 2);
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final var wrapper1 = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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final var wrapper2 = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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assertEquals(wrapper1.hashCode(), wrapper2.hashCode());
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}
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/**
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* Tests GcdSolutionWrapper toString.
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*/
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@Test
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void testGcdSolutionWrapperToString() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(1, 2);
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final var wrapper = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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final var str = wrapper.toString();
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assertTrue(str.contains("5"));
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assertTrue(str.contains("GcdSolutionWrapper"));
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}
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/**
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* Tests Equation record functionality.
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*/
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@Test
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void testEquationRecord() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(3, 4, 7);
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assertEquals(3, equation.a());
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assertEquals(4, equation.b());
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assertEquals(7, equation.c());
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}
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/**
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* Tests an equation with c = 0: 3x + 4y = 0.
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* Expected solution: x = 0, y = 0.
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*/
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@Test
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void testZeroResult() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(3, 4, 0);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests Solution setters.
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*/
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@Test
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void testSolutionSetters() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(1, 2);
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solution.setX(10);
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solution.setY(20);
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assertEquals(10, solution.getX());
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assertEquals(20, solution.getY());
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}
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/**
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* Tests GcdSolutionWrapper setters.
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*/
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@Test
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void testGcdSolutionWrapperSetters() {
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final var solution = new LinearDiophantineEquationsSolver.Solution(1, 2);
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final var wrapper = new LinearDiophantineEquationsSolver.GcdSolutionWrapper(5, solution);
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final var newSolution = new LinearDiophantineEquationsSolver.Solution(3, 4);
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wrapper.setGcd(10);
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wrapper.setSolution(newSolution);
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assertEquals(10, wrapper.getGcd());
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assertEquals(newSolution, wrapper.getSolution());
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}
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/**
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* Tests an equation with both coefficients negative: -3x - 4y = -7.
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*/
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@Test
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void testBothCoefficientsNegative() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(-3, -4, -7);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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/**
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* Tests an equation with large prime coefficients: 97x + 101y = 198.
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*/
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@Test
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void testLargePrimeCoefficients() {
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final var equation = new LinearDiophantineEquationsSolver.Equation(97, 101, 198);
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final var solution = LinearDiophantineEquationsSolver.findAnySolution(equation);
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assertNotNull(solution);
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int result = equation.a() * solution.getX() + equation.b() * solution.getY();
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assertEquals(equation.c(), result);
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}
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}
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