Added solutions 12. & 13., Int to Roman & Roman to Int (#76)

* Added solutions for Integer to Roman (q. 12) and Roman to Integer (q. 13)

* Updated README.md

* Removed main methods

Author: Kingal1337

Java/integer-to-roman.java

@@ -0,0 +1,60 @@
+public class IntegerToRoman{
+    public static String numberToRoman(int number){//Converts a number into a roman numerial
+        String roman = "";
+        while(number != 0){//checks if the number is not equal to 0, if it is not equal then there is more processing to be done
+            if(number >= 1000){//if the number is larger than 1000, then add an M to the roman string and subtract 1000 from number
+                roman += "M";
+                number -= 1000;
+            }
+            else if(number >= 900){//if the number is larger than 900, then add an CM to the roman string and subtract 900 from number
+                roman += "CM";
+                number -= 900;
+            }
+            else if(number >= 500){//if the number is larger than 500, then add an D to the roman string and subtract 500 from number
+                roman += "D";
+                number -= 500;
+            }
+            else if(number >= 400){//if the number is larger than 400, then add an CD to the roman string and subtract 400 from number
+                roman += "CD";
+                number -= 400;
+            }
+            else if(number >= 100){//if the number is larger than 100, then add an C to the roman string and subtract 100 from number
+                roman += "C";
+                number -= 100;
+            }
+            else if(number >= 90){//if the number is larger than 90, then add an XC to the roman string and subtract 90 from number
+                roman += "XC";
+                number -= 90;
+            }
+            else if(number >= 50){//if the number is larger than 50, then add an L to the roman string and subtract 50 from number
+                roman += "L";
+                number -= 50;
+            }
+            else if(number >= 40){//if the number is larger than 40, then add an XL to the roman string and subtract 40 from number
+                roman += "XL";
+                number -= 40;
+            }
+            else if(number >= 10){//if the number is larger than 10, then add an X to the roman string and subtract 10 from number
+                roman += "X";
+                number -= 10;
+            }
+            else if(number >= 9){//if the number is larger than 9, then add an IX to the roman string and subtract 9 from number
+                roman += "IX";
+                number -= 9;
+            }
+            else if(number >= 5){//if the number is larger than 5, then add an V to the roman string and subtract 5 from number
+                roman += "V";
+                number -= 5;
+            }
+            else if(number >= 4){//if the number is larger than 4, then add an IV to the roman string and subtract 4 from number
+                roman += "IV";
+                number -= 4;
+            }
+            else if(number >= 1){//if the number is larger than 1, then add an I to the roman string and subtract 1 from number
+                roman += "I";
+                number -= 1;
+            }
+        }
+        return roman;
+    }
+}

Java/roman-to-integer.java

@@ -0,0 +1,54 @@
+public class RomanToInteger{
+    public static int GetNum(int num) {//gets the number assoicate with a roman character
+        if (num == 'I' || num == 'i') {
+            return 1;
+        }
+        if (num == 'V' || num == 'v') {
+            return 5;
+        }
+        if (num == 'X' || num == 'x') {
+            return 10;
+        }
+        if (num == 'L' || num == 'l') {
+            return 50;
+        }
+        if (num == 'C' || num == 'c') {
+            return 100;
+        }
+        if (num == 'D' || num == 'd') {
+            return 500;
+        }
+        if (num == 'M' || num == 'm') {
+            return 1000;
+        }
+
+        return -1;
+    }
+
+    public static int romanToNumber(String roman){//Converts a roman numerial into a number
+        int results = 0;
+        for (int i = 0; i < roman.length(); i++) {//iterate through all the characters
+            int cur = GetNum(roman.charAt(i));//Gets the integer of the roman number
+            if (cur == -1) {//checks if the cur num is -1, if it is -1, it means that it is an invalid character
+                return -1;
+            }
+            if (i + 1 < roman.length()) {//checks if the next index is out of bounds
+                int next = GetNum(roman.charAt(i + 1));//gets the next character character
+                if (next == -1) {//checks if the cur num is -1, if it is -1, it means that it is an invalid character
+                    return -1;
+                }
+                if (cur >= next) {//compares the current number to the next number
+                    results += cur;//if it is bigger, simply add the current number
+                }
+                else {//if the current number is smaller than the next number
+                    results += (next - cur);//subtract the next number by the current number
+                    i++;//increment the index, since the next number has already been used
+                }
+            }
+            else {//only here to add the last number to the results
+                results += cur;//adds the last character to the results
+            }
+        }
+        return results;//returns the result
+    }
+}

README.md

@@ -246,7 +246,9 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 168 | [Excel Sheet Column Title](https://leetcode.com/problems/excel-sheet-column-title) | [C++](./C++/Excel-Sheet-Column-Title.cpp)                                 | _O(n)_            | _O(n)_ | Easy       | String |      |
 | 007 | [Reverse Integer](https://leetcode.com/problems/reverse-integer)                   | [Java](./Java/reverse-integer.java) <br> [C++](./C++/Reverse-Integer.cpp) | _O(n)_            | _O(n)_ | Easy       | Math   |      |
 | 202 | [Happy Number](https://leetcode.com/problems/happy-number)                         | [Java](./Java/Happy-Number.java)                                          | _O(n^2)_          | _O(n)_ | Easy       | Math   |      |
-| 326 | [Power of Three](https://leetcode.com/problems/power-of-three)                         | [Java](./Java/Power-of-Three.java)                                         | _O(logn)_          | _O(n)_ | Easy       | Math   |      |
+| 326 | [Power of Three](https://leetcode.com/problems/power-of-three)                     | [Java](./Java/Power-of-Three.java)                                         | _O(logn)_          | _O(n)_ | Easy       | Math   |      |
+| 12  | [Integer to Roman](https://leetcode.com/problems/integer-to-roman)                 | [Java](./Java/integer-to-roman.java)                                      | _O(n)_          | _O(1)_ | Medium       | Math   |      |
+| 13  | [Roman to Integer](https://leetcode.com/problems/roman-to-integer)                 | [Java](./Java/roman-to-integer.java)                                      | _O(n)_          | _O(1)_ | Easy       | Math   |      |
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