feat: add conversion logic from integer to english (#5540)

* feat: add conversion logic from integer to english

* feat: update DIRECTORY.md

* feat: fix linting issues

* feat: fix build issue

* feat: address review comments

---------

Co-authored-by: sailok.chinta <[email protected]>
Co-authored-by: Alex Klymenko <[email protected]>

Author: 3 people

DIRECTORY.md

@@ -68,6 +68,7 @@
             * [HexaDecimalToBinary](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java)
             * [HexaDecimalToDecimal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/HexaDecimalToDecimal.java)
             * [HexToOct](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/HexToOct.java)
+            * [IntegerToEnglish] (https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/IntegerToEnglish.java)
             * [IntegerToRoman](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/IntegerToRoman.java)
             * [OctalToBinary](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/OctalToBinary.java)
             * [OctalToDecimal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/conversions/OctalToDecimal.java)

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

@@ -0,0 +1,80 @@
+package com.thealgorithms.conversions;
+
+import java.util.Map;
+
+public final class IntegerToEnglish {
+    private static final Map<Integer, String> BASE_NUMBERS_MAP = Map.ofEntries(Map.entry(0, ""), Map.entry(1, "One"), Map.entry(2, "Two"), Map.entry(3, "Three"), Map.entry(4, "Four"), Map.entry(5, "Five"), Map.entry(6, "Six"), Map.entry(7, "Seven"), Map.entry(8, "Eight"), Map.entry(9, "Nine"),
+        Map.entry(10, "Ten"), Map.entry(11, "Eleven"), Map.entry(12, "Twelve"), Map.entry(13, "Thirteen"), Map.entry(14, "Fourteen"), Map.entry(15, "Fifteen"), Map.entry(16, "Sixteen"), Map.entry(17, "Seventeen"), Map.entry(18, "Eighteen"), Map.entry(19, "Nineteen"), Map.entry(20, "Twenty"),
+        Map.entry(30, "Thirty"), Map.entry(40, "Forty"), Map.entry(50, "Fifty"), Map.entry(60, "Sixty"), Map.entry(70, "Seventy"), Map.entry(80, "Eighty"), Map.entry(90, "Ninety"), Map.entry(100, "Hundred"));
+
+    private static final Map<Integer, String> THOUSAND_POWER_MAP = Map.ofEntries(Map.entry(1, "Thousand"), Map.entry(2, "Million"), Map.entry(3, "Billion"));
+
+    private IntegerToEnglish() {
+    }
+
+    /**
+        converts numbers < 1000 to english words
+     */
+    private static String convertToWords(int number) {
+        int remainder = number % 100;
+
+        String result;
+
+        if (remainder <= 20) {
+            result = BASE_NUMBERS_MAP.get(remainder);
+        } else if (BASE_NUMBERS_MAP.containsKey(remainder)) {
+            result = BASE_NUMBERS_MAP.get(remainder);
+        } else {
+            int tensDigit = remainder / 10;
+            int onesDigit = remainder % 10;
+
+            result = String.format("%s %s", BASE_NUMBERS_MAP.get(tensDigit * 10), BASE_NUMBERS_MAP.get(onesDigit));
+        }
+
+        int hundredsDigit = number / 100;
+
+        if (hundredsDigit > 0) {
+            result = String.format("%s %s%s", BASE_NUMBERS_MAP.get(hundredsDigit), BASE_NUMBERS_MAP.get(100), result.isEmpty() ? "" : " " + result);
+        }
+
+        return result;
+    }
+
+    /**
+      Only convert groups of three digit if they are non-zero
+     */
+    public static String integerToEnglishWords(int number) {
+        if (number == 0) {
+            return "Zero";
+        }
+
+        StringBuilder result = new StringBuilder();
+
+        int index = 0;
+
+        while (number > 0) {
+            int remainder = number % 1000;
+            number /= 1000;
+
+            if (remainder > 0) {
+                String subResult = convertToWords(remainder);
+
+                if (!subResult.isEmpty()) {
+                    if (!result.isEmpty()) {
+                        result.insert(0, subResult + " " + THOUSAND_POWER_MAP.get(index) + " ");
+                    } else {
+                        if (index > 0) {
+                            result = new StringBuilder(subResult + " " + THOUSAND_POWER_MAP.get(index));
+                        } else {
+                            result = new StringBuilder(subResult);
+                        }
+                    }
+                }
+            }
+
+            index++;
+        }
+
+        return result.toString();
+    }
+}

src/test/java/com/thealgorithms/conversions/IntegerToEnglishTest.java

@@ -0,0 +1,15 @@
+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class IntegerToEnglishTest {
+
+    @Test
+    public void testIntegerToEnglish() {
+        assertEquals("Two Billion One Hundred Forty Seven Million Four Hundred Eighty Three Thousand Six Hundred Forty Seven", IntegerToEnglish.integerToEnglishWords(2147483647));
+        assertEquals("One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven", IntegerToEnglish.integerToEnglishWords(1234567));
+        assertEquals("Twelve Thousand Three Hundred Forty Five", IntegerToEnglish.integerToEnglishWords(12345));
+    }
+}