feat: add conversion logic from integer to english

DIRECTORY.md

@@ -67,6 +67,7 @@
             * [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 +1,116 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+
+public final class IntegerToEnglish {
+    private static final HashMap<Integer, String> BASE_NUMBERS_MAP = new HashMap<>() {
+        {
+            put(0, "");
+            put(1, "One");
+            put(2, "Two");
+            put(3, "Three");
+            put(4, "Four");
+            put(5, "Five");
+            put(6, "Six");
+            put(7, "Seven");
+            put(8, "Eight");
+            put(9, "Nine");
+            put(10, "Ten");
+            put(11, "Eleven");
+            put(12, "Twelve");
+            put(13, "Thirteen");
+            put(14, "Fourteen");
+            put(15, "Fifteen");
+            put(16, "Sixteen");
+            put(17, "Seventeen");
+            put(18, "Eighteen");
+            put(19, "Nineteen");
+            put(20, "Twenty");
+            put(30, "Thirty");
+            put(40, "Forty");
+            put(50, "Fifty");
+            put(60, "Sixty");
+            put(70, "Seventy");
+            put(80, "Eighty");
+            put(90, "Ninety");
+            put(100, "Hundred");
+        }
+    };
+
+    private static final HashMap<Integer, String> THOUSAND_POWER_MAP = new HashMap<>() {
+        {
+            put(1, "Thousand");
+            put(2, "Million");
+            put(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));
+    }
+}