iSharkFly-Docs/java-tutorials
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

List all factors of a number in Java (#12646)

Browse Source 
* List all factors of a number in Java

* format the map code in the test
This commit is contained in:
Kai Yuan 2022-08-27 03:26:38 +02:00 committed by GitHub
parent 46499a2419
commit 0ea458117e
2 changed files with 79 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
core-java-modules/core-java-numbers-5/src/main/java/com/baeldung/factors/FactorsOfInteger.java Normal file
View File

@ -0,0 +1,39 @@
package com.baeldung.factors;
import java.util.HashSet;
import java.util.Set;
public class FactorsOfInteger {
public static Set<Integer> getAllFactorsVer1(int n) {
Set<Integer> factors = new HashSet<>();
for (int i = 1; i <= n; i++) {
if (n % i == 0) {
factors.add(i);
}
}
return factors;
}
public static Set<Integer> getAllFactorsVer2(int n) {
Set<Integer> factors = new HashSet<>();
for (int i = 1; i <= Math.sqrt(n); i++) {
if (n % i == 0) {
factors.add(i);
factors.add(n / i);
}
}
return factors;
}
public static Set<Integer> getAllFactorsVer3(int n) {
Set<Integer> factors = new HashSet<>();
int step = n % 2 == 0 ? 1 : 2;
for (int i = 1; i <= Math.sqrt(n); i += step) {
if (n % i == 0) {
factors.add(i);
factors.add(n / i);
}
}
return factors;
}
}

40
core-java-modules/core-java-numbers-5/src/test/java/com/baeldung/factors/FactorsOfIntegerUnitTest.java Normal file
View File

@ -0,0 +1,40 @@
package com.baeldung.factors;
import static org.junit.jupiter.api.Assertions.assertEquals;
import java.util.Map;
import java.util.Set;
import org.junit.jupiter.api.Test;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
class FactorsOfIntegerUnitTest {
//@formatter:off
private final static Map<Integer, Set<Integer>> FACTOR_MAP = ImmutableMap.of(
0, ImmutableSet.of(),
1, ImmutableSet.of(1),
20, ImmutableSet.of(1, 2, 4, 5, 10, 20),
24, ImmutableSet.of(1, 2, 3, 4, 6, 8, 12, 24),
97, ImmutableSet.of(1, 97),
99, ImmutableSet.of(1, 3, 9, 11, 33, 99),
100, ImmutableSet.of(1, 2, 4, 5, 10, 20, 25, 50, 100)
);
//@formatter:on
@Test
void givenAnInteger_whenCallingFindAllFactorsTheDraftVersion_shouldGetExpectedResult() {
FACTOR_MAP.forEach((number, expected) -> assertEquals(expected, FactorsOfInteger.getAllFactorsVer1(number)));
}
@Test
void givenAnInteger_whenCallingFindAllFactorsVer2_shouldGetExpectedResult() {
FACTOR_MAP.forEach((number, expected) -> assertEquals(expected, FactorsOfInteger.getAllFactorsVer2(number)));
}
@Test
void givenAnInteger_whenCallingFindAllFactorsVer3_shouldGetExpectedResult() {
FACTOR_MAP.forEach((number, expected) -> assertEquals(expected, FactorsOfInteger.getAllFactorsVer3(number)));
}
}