solves integer to roman

Author: anishLearnsToCode

README.md

@@ -20,6 +20,7 @@
 |  8   | [String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi)                                                                          |                                                               [![Java](assets/java.png)](src/StringToIntegerAtoi.java)                                                               |                                                                                                                                   |
 |  9   | [PalindromeNumber](https://leetcode.com/problems/palindrome-number/)                                                                                      |                                  [![Java](assets/java.png)](src/PalindromeNumber.java) [![Python](assets/python.png)](python/palindrome_number.py)                                   |                                                                                                                                   |
 |  11  | [Container With Most Water](https://leetcode.com/problems/container-with-most-water)                                                                      |                                                              [![Java](assets/java.png)](src/ContainerWitMostWater.java)                                                              |                                                                                                                                   |
+|  12  | [Integer to Roman](https://leetcode.com/problems/integer-to-roman)                                                                                        |                                                                 [![Java](assets/java.png)](src/IntegerToRoman.java)                                                                  |                                                                                                                                   |
 |  13  | [Roman To Integer](https://leetcode.com/problems/roman-to-integer/)                                                                                       |                                    [![Java](assets/java.png)](src/RomanToInteger.java) [![Python](assets/python.png)](python/roman_to_integer.py)                                    | [![java-yt](assets/java-yt.png)](https://youtu.be/BCue_mO_81A) [![python-yt](assets/python-yt.png)](https://youtu.be/8h_yGTNvKMA) |
 |  14  | [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)                                                                             |                               [![Java](assets/java.png)](src/LongestCommonPrefix.java) [![Python](assets/python.png)](python/longest_common_prefix.py)                               |                                                                                                                                   |
 |  20  | [ValidParentheses](https://leetcode.com/problems/valid-parentheses/)                                                                                      |                                  [![Java](assets/java.png)](src/ValidParentheses.java) [![Python](assets/python.png)](python/valid_parentheses.py)                                   |                                                                                                                                   |

src/IntegerToRoman.java

@@ -0,0 +1,62 @@
+// https://leetcode.com/problems/integer-to-roman
+// T: O(log n)
+// S: O(log n)
+
+import java.util.Map;
+
+public class IntegerToRoman {
+    private final static int ONE = 1;
+    private final static int FIVE = 5;
+    private final static int TEN = 10;
+
+    private final static Map<Integer, String> ONES_PLACE_ROMAN_CHARS = Map.ofEntries(
+            Map.entry(ONE, "I"),
+            Map.entry(FIVE, "V"),
+            Map.entry(TEN, "X")
+    );
+
+    private final static Map<Integer, String> TENS_PLACE_ROMAN_CHARS = Map.ofEntries(
+            Map.entry(ONE, "X"),
+            Map.entry(FIVE, "L"),
+            Map.entry(TEN, "C")
+    );
+
+    private final static Map<Integer, String> HUNDREDS_PLACE_ROMAN_CHARS = Map.ofEntries(
+            Map.entry(ONE, "C"),
+            Map.entry(FIVE, "D"),
+            Map.entry(TEN, "M")
+    );
+
+    public String intToRoman(int num) {
+        final StringBuilder result = new StringBuilder();
+        for (int place = 1000 ; num > 0 ; place /= 10) {
+            result.append(toRoman(num / place, place));
+            num -= (num / place) * place;
+        }
+        return result.toString();
+    }
+
+    private String toRoman(int digit, int place) {
+        return switch (place) {
+            case 1 -> toRomanFromPlace(digit, ONES_PLACE_ROMAN_CHARS);
+            case 10 -> toRomanFromPlace(digit, TENS_PLACE_ROMAN_CHARS);
+            case 100 -> toRomanFromPlace(digit, HUNDREDS_PLACE_ROMAN_CHARS);
+            case 1000 -> thousandsPlaceToRoman(digit);
+            default -> "";
+        };
+    }
+
+    private String toRomanFromPlace(int digit, Map<Integer, String> romanChars) {
+        return switch (digit) {
+            case 1, 2, 3 -> romanChars.get(ONE).repeat(digit);
+            case 4 -> romanChars.get(ONE) + romanChars.get(FIVE);
+            case 5, 6, 7, 8 -> romanChars.get(FIVE) + romanChars.get(ONE).repeat(digit - 1);
+            case 9 -> romanChars.get(ONE) + romanChars.get(TEN);
+            default -> "";
+        };
+    }
+
+    private String thousandsPlaceToRoman(int digit) {
+        return "M".repeat(digit);
+    }
+}