Updated 1 solution

Author: RodneyShag

Chp. 16 - More Problems (Moderate)/_16_08_English_Int/EnglishInt.java

@@ -3,16 +3,15 @@
 // Solution is mostly from online book solutions 
 //
 // Tricks:
-// - use arrays as data structure for the words
-// - split at the commas of a long number (into groups of 3), using a function called "numToStringl00"
-// - don't forget to consider negative numbers
+// - Use arrays as data structure for the words.
+// - Split the number at each comma into groups of 3 digits. Create a function to convert 3-digit numbers to words.
+// - Don't forget to consider negative numbers, and 0.
 
 public class EnglishInt {
 
- private static String[] digits = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
- private static String[] teens = {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
- private static String[] tens = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
- private static String[] bigs = {"", "Thousand", "Million", "Billion"};
+ private static String[] first20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
+ private static String[] tens = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
+ private static String[] bigs = {"", "Thousand", "Million", "Billion"};
 
  public static String numToString(int num) {
  if (num < 0) {
@@ -24,53 +23,28 @@ public static String numToString(int num) {
  int bigsIndex = 0;
  StringBuffer sb = new StringBuffer();
 
- /* We create the string from right to left, inserting in the front. This makes code clean and scalability easier */
+ // We create the string from right to left, inserting in the front. This makes code clean and scalability easier
  while (num > 0) {
  if (num % 1000 != 0) {
  sb.insert(0, numToString100(num % 1000) + bigs[bigsIndex] + " ");
  }
  num /= 1000;
  bigsIndex++;
  }
- return sb.toString();
+ return sb.toString().trim();
  }
 
- public static String numToString100(int num) {
- if (num < 0) {
- return "Negative " + numToString(-1 * num);
- } else if (num == 0) {
- return "Zero";
- } else if (num > 999) {
- return null;
- }
-
- StringBuffer sb = new StringBuffer();
-
- /* Hundreds */
- if (num >= 100) {
- int digit = num / 100;
- sb.append(digits[digit] + " Hundred ");
- num = num % 100; // now we have a 2-digit number
- }
-
- /* Tens */
- int tensDigit = num / 10;
- int singleDigit = num % 10;
-
- if (num >= 10 && num <= 19) {
- sb.append(teens[singleDigit] + " ");
- return sb.toString();
- } else if (num >= 20) {
- sb.append(tens[tensDigit] + " ");
- }
-
- /* Single Digit */
- if (singleDigit != 0) {
- sb.append(digits[singleDigit] + " ");
- }
-
- return sb.toString();
+ private static String numToString100(int num) { // assumes 0 < num < 1000
+ if (num == 0)
+ return "";
+ else if (num < 20)
+ return first20[num] + " ";
+ else if (num < 100)
+ return tens[num / 10] + " " + numToString100(num % 10);
+ else
+ return first20[num / 100] + " Hundred " + numToString100(num % 100);
  }
 }
 
-// Time Complexity: O(1)
+// Time Complexity: O(1)
+// Space Complexity: O(1)

Chp. 16 - More Problems (Moderate)/_16_08_English_Int/Tester.java

@@ -6,9 +6,11 @@ public static void main(String[] args) {
  for (int i = 0; i < 23; i++) {
  test(i);
  }
+ test(0);
  test(1000);
- test(2998);
+ test(-2998);
  test(253513);
+ test(1000010);
  test(10090034);
  }