Add convertion of numbers into their word representation (#6137)

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

@@ -0,0 +1,100 @@
+package com.thealgorithms.conversions;
+
+import java.math.BigDecimal;
+
+/**
+ A Java-based utility for converting numeric values into their English word
+ representations. Whether you need to convert a small number, a large number
+ with millions and billions, or even a number with decimal places, this utility
+ has you covered.
+ *
+ */
+public final class NumberToWords {
+
+    private NumberToWords() {
+    }
+
+    private static final String[] UNITS = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
+
+    private static final String[] TENS = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
+
+    private static final String[] POWERS = {"", "Thousand", "Million", "Billion", "Trillion"};
+
+    private static final String ZERO = "Zero";
+    private static final String POINT = " Point";
+    private static final String NEGATIVE = "Negative ";
+
+    public static String convert(BigDecimal number) {
+        if (number == null) {
+            return "Invalid Input";
+        }
+
+        // Check for negative sign
+        boolean isNegative = number.signum() < 0;
+
+        // Split the number into whole and fractional parts
+        BigDecimal[] parts = number.abs().divideAndRemainder(BigDecimal.ONE);
+        BigDecimal wholePart = parts[0]; // Keep whole part as BigDecimal
+        String fractionalPartStr = parts[1].compareTo(BigDecimal.ZERO) > 0 ? parts[1].toPlainString().substring(2) : ""; // Get fractional part only if it exists
+
+        // Convert whole part to words
+        StringBuilder result = new StringBuilder();
+        if (isNegative) {
+            result.append(NEGATIVE);
+        }
+        result.append(convertWholeNumberToWords(wholePart));
+
+        // Convert fractional part to words
+        if (!fractionalPartStr.isEmpty()) {
+            result.append(POINT);
+            for (char digit : fractionalPartStr.toCharArray()) {
+                int digitValue = Character.getNumericValue(digit);
+                result.append(" ").append(digitValue == 0 ? ZERO : UNITS[digitValue]);
+            }
+        }
+
+        return result.toString().trim();
+    }
+
+    private static String convertWholeNumberToWords(BigDecimal number) {
+        if (number.compareTo(BigDecimal.ZERO) == 0) {
+            return ZERO;
+        }
+
+        StringBuilder words = new StringBuilder();
+        int power = 0;
+
+        while (number.compareTo(BigDecimal.ZERO) > 0) {
+            // Get the last three digits
+            BigDecimal[] divisionResult = number.divideAndRemainder(BigDecimal.valueOf(1000));
+            int chunk = divisionResult[1].intValue();
+
+            if (chunk > 0) {
+                String chunkWords = convertChunk(chunk);
+                if (power > 0) {
+                    words.insert(0, POWERS[power] + " ");
+                }
+                words.insert(0, chunkWords + " ");
+            }
+
+            number = divisionResult[0]; // Continue with the remaining part
+            power++;
+        }
+
+        return words.toString().trim();
+    }
+
+    private static String convertChunk(int number) {
+        String chunkWords;
+
+        if (number < 20) {
+            chunkWords = UNITS[number];
+        } else if (number < 100) {
+            chunkWords = TENS[number / 10] + (number % 10 > 0 ? " " + UNITS[number % 10] : "");
+        } else {
+            chunkWords = UNITS[number / 100] + " Hundred" + (number % 100 > 0 ? " " + convertChunk(number % 100) : "");
+        }
+
+        return chunkWords;
+    }
+}