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Merge pull request #16274 from thibaultfaure/articles/BAEL-7657-Date-of-Easter-Sunday 

BAEL-7657 Code for the Find the date of Easter Sunday for the given y…
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Vini 2024-04-16 15:34:56 +02:00 committed by GitHub
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76
algorithms-modules/algorithms-miscellaneous-8/src/main/java/com/baeldung/algorithms/eastersunday/EasterDateCalculator.java Normal file
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package com.baeldung.algorithms.eastersunday;
import java.time.LocalDate;
public class EasterDateCalculator {
LocalDate computeEasterDateWithGaussAlgorithm(int year) {
int a = year % 19;
int b = year % 4;
int c = year % 7;
int k = year / 100;
int p = (13 + 8*k) / 25;
int q = k / 4;
int M = (15 - p + k - q) % 30;
int N = (4 + k - q) % 7;
int d = (19*a + M) % 30;
int e = (2*b + 4*c + 6*d + N) % 7;
if (d==29 && e == 6) {
return LocalDate.of(year, 4, 19);
} else if (d==28 && e==6 && ((11*M + 11)%30 < 10)) {
return LocalDate.of(year, 4, 18);
}
int H = 22 + d + e;
if (H <= 31) {
return LocalDate.of(year, 3, H);
}
return LocalDate.of(year, 4, H-31);
}
LocalDate computeEasterDateWithButcherMeeusAlgorithm(int year) {
int a = year % 19;
int b = year / 100;
int c = year % 100;
int d = b / 4;
int e = b % 4;
int f = (b + 8) / 25;
int g = (b - f + 1) / 3;
int h = (19*a + b - d - g + 15) % 30;
int i = c / 4;
int k = c % 4;
int l = (2*e + 2*i - h - k + 32) % 7;
int m = (a + 11*h + 22*l) / 451;
int t = h + l - 7*m + 114;
int n = t / 31;
int o = t % 31;
return LocalDate.of(year, n, o+1);
}
LocalDate computeEasterDateWithConwayAlgorithm(int year) {
int s = year / 100;
int t = year % 100;
int a = t / 4;
int p = s % 4;
int x = (9 - 2*p) % 7;
int y = (x + t + a) % 7;
int g = year % 19;
int G = g + 1;
int b = s / 4;
int r = 8 * (s + 11) / 25;
int C = -s + b + r;
int d = (11*G + C) % 30;
d = (d + 30) % 30;
int h = (551 - 19*d + G) / 544;
int e = (50 - d - h) % 7;
int f = (e + y) % 7;
int R = 57 - d - f - h;
if (R <= 31) {
return LocalDate.of(year, 3, R);
}
return LocalDate.of(year, 4, R-31);
}
}

53
algorithms-modules/algorithms-miscellaneous-8/src/test/java/com/baeldung/algorithms/eastersunday/EasterDateCalculatorUnitTest.java Normal file
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package com.baeldung.algorithms.eastersunday;
import static org.junit.jupiter.api.Assertions.assertEquals;
import java.time.LocalDate;
import org.junit.jupiter.api.Test;
public class EasterDateCalculatorUnitTest {
@Test
void givenEasterInMarch_whenComputeEasterDateWithGaussAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2024, 3, 31), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(2024));
}
@Test
void givenEasterInApril_whenComputeEasterDateWithGaussAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2004, 4, 11), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(2004));
}
@Test
void givenEdgeCases_whenComputeEasterDateWithGaussAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(1981, 4, 19), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1981));
assertEquals(LocalDate.of(1954, 4, 18), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1954));
}
@Test
void givenEasterInMarch_whenComputeEasterDateWithButcherMeeusAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2024, 3, 31), new EasterDateCalculator().computeEasterDateWithButcherMeeusAlgorithm(2024));
}
@Test
void givenEasterInApril_whenComputeEasterDateWithButcherMeeusAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2004, 4, 11), new EasterDateCalculator().computeEasterDateWithButcherMeeusAlgorithm(2004));
// The following are added just to notice that there is no need for a special case with this algorithm
assertEquals(LocalDate.of(1981, 4, 19), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1981));
assertEquals(LocalDate.of(1954, 4, 18), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1954));
}
@Test
void givenEasterInMarch_whenComputeEasterDateWithConwayAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2024, 3, 31), new EasterDateCalculator().computeEasterDateWithConwayAlgorithm(2024));
}
@Test
void givenEasterInApril_whenComputeEasterDateWithConwayAlgorithm_thenCorrectResult() {
assertEquals(LocalDate.of(2004, 4, 11), new EasterDateCalculator().computeEasterDateWithConwayAlgorithm(2004));
// The following are added just to notice that there is no need for a special case with this algorithm
assertEquals(LocalDate.of(1981, 4, 19), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1981));
assertEquals(LocalDate.of(1954, 4, 18), new EasterDateCalculator().computeEasterDateWithGaussAlgorithm(1954));
}
}