feat: add temperature unit conversions (#5315)

Co-authored-by: Bama Charan Chhandogi <b.c.chhandogi@gmail.com>

src/main/java/com/thealgorithms/conversions/AffineConverter.java

@@ -0,0 +1,23 @@
+package com.thealgorithms.conversions;
+
+public final class AffineConverter {
+    private final double slope;
+    private final double intercept;
+    public AffineConverter(final double inSlope, final double inIntercept) {
+        slope = inSlope;
+        intercept = inIntercept;
+    }
+
+    public double convert(final double inValue) {
+        return slope * inValue + intercept;
+    }
+
+    public AffineConverter invert() {
+        assert slope != 0.0;
+        return new AffineConverter(1.0 / slope, -intercept / slope);
+    }
+
+    public AffineConverter compose(final AffineConverter other) {
+        return new AffineConverter(slope * other.slope, slope * other.intercept + intercept);
+    }
+}

src/main/java/com/thealgorithms/conversions/UnitConversions.java

@@ -0,0 +1,14 @@
+package com.thealgorithms.conversions;
+
+import static java.util.Map.entry;
+
+import java.util.Map;
+import org.apache.commons.lang3.tuple.Pair;
+
+public final class UnitConversions {
+    private UnitConversions() {
+    }
+
+    public static final UnitsConverter TEMPERATURE = new UnitsConverter(Map.ofEntries(entry(Pair.of("Kelvin", "Celsius"), new AffineConverter(1.0, -273.15)), entry(Pair.of("Celsius", "Fahrenheit"), new AffineConverter(9.0 / 5.0, 32.0)),
+        entry(Pair.of("Réaumur", "Celsius"), new AffineConverter(5.0 / 4.0, 0.0)), entry(Pair.of("Delisle", "Celsius"), new AffineConverter(-2.0 / 3.0, 100.0)), entry(Pair.of("Rankine", "Kelvin"), new AffineConverter(5.0 / 9.0, 0.0))));
+}

src/main/java/com/thealgorithms/conversions/UnitsConverter.java

@@ -0,0 +1,86 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import org.apache.commons.lang3.tuple.Pair;
+
+public final class UnitsConverter {
+    private final Map<Pair<String, String>, AffineConverter> conversions;
+    private final Set<String> units;
+
+    private static void putIfNeeded(Map<Pair<String, String>, AffineConverter> conversions, final String inputUnit, final String outputUnit, final AffineConverter converter) {
+        if (!inputUnit.equals(outputUnit)) {
+            final var key = Pair.of(inputUnit, outputUnit);
+            conversions.putIfAbsent(key, converter);
+        }
+    }
+
+    private static Map<Pair<String, String>, AffineConverter> addInversions(final Map<Pair<String, String>, AffineConverter> knownConversions) {
+        Map<Pair<String, String>, AffineConverter> res = new HashMap<Pair<String, String>, AffineConverter>();
+        for (final var curConversion : knownConversions.entrySet()) {
+            final var inputUnit = curConversion.getKey().getKey();
+            final var outputUnit = curConversion.getKey().getValue();
+            putIfNeeded(res, inputUnit, outputUnit, curConversion.getValue());
+            putIfNeeded(res, outputUnit, inputUnit, curConversion.getValue().invert());
+        }
+        return res;
+    }
+
+    private static Map<Pair<String, String>, AffineConverter> addCompositions(final Map<Pair<String, String>, AffineConverter> knownConversions) {
+        Map<Pair<String, String>, AffineConverter> res = new HashMap<Pair<String, String>, AffineConverter>();
+        for (final var first : knownConversions.entrySet()) {
+            final var firstKey = first.getKey();
+            putIfNeeded(res, firstKey.getKey(), firstKey.getValue(), first.getValue());
+            for (final var second : knownConversions.entrySet()) {
+                final var secondKey = second.getKey();
+                if (firstKey.getValue().equals(secondKey.getKey())) {
+                    final var newConversion = second.getValue().compose(first.getValue());
+                    putIfNeeded(res, firstKey.getKey(), secondKey.getValue(), newConversion);
+                }
+            }
+        }
+        return res;
+    }
+
+    private static Map<Pair<String, String>, AffineConverter> addAll(final Map<Pair<String, String>, AffineConverter> knownConversions) {
+        final var res = addInversions(knownConversions);
+        return addCompositions(res);
+    }
+
+    private static Map<Pair<String, String>, AffineConverter> computeAllConversions(final Map<Pair<String, String>, AffineConverter> basicConversions) {
+        var tmp = basicConversions;
+        var res = addAll(tmp);
+        while (res.size() != tmp.size()) {
+            tmp = res;
+            res = addAll(tmp);
+        }
+        return res;
+    }
+
+    private static Set<String> extractUnits(final Map<Pair<String, String>, AffineConverter> conversions) {
+        Set<String> res = new HashSet<>();
+        for (final var conversion : conversions.entrySet()) {
+            res.add(conversion.getKey().getKey());
+        }
+        return res;
+    }
+
+    public UnitsConverter(final Map<Pair<String, String>, AffineConverter> basicConversions) {
+        conversions = computeAllConversions(basicConversions);
+        units = extractUnits(conversions);
+    }
+
+    public double convert(final String inputUnit, final String outputUnit, final double value) {
+        if (inputUnit.equals(outputUnit)) {
+            throw new IllegalArgumentException("inputUnit must be different from outputUnit.");
+        }
+        final var conversionKey = Pair.of(inputUnit, outputUnit);
+        return conversions.get(conversionKey).convert(value);
+    }
+
+    public Set<String> availableUnits() {
+        return units;
+    }
+}