chore(Java) : add roman numerals conversion (#849)
* Add Roman Numerals Conversion * roman numerals conversion, expanded description * roman numerals conversion, expanded descriptionpull/865/head
Vivi Koutsoumanidou
GitHub
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b4cd97f55a
commit
62907b69ec
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import java.util.HashMap;
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/**
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* Problem: To convert an integer to its Roman numeral equivalent and vice versa.
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* ----------------------------------------------------------------------------------------------------------------
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*
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* Time Complexity: O(n)
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* Space Complexity: O(1)
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*
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* ----------------------------------------------------------------------------------------------------------------
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*
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* Constraints:
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* The input sting should contain only the characters ('I', 'V', 'X', 'L', 'C', 'D', 'M').
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* It is guaranteed that the input is a valid roman numeral in the range [1, 3999].
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*
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* ----------------------------------------------------------------------------------------------------------------
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*
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* Description:
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* There are seven basic different symbols to represent roman numerals: I, V, X, L, C, D and M.
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* Those being:
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* Symbol Value
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* I 1
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* V 5
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* X 10
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* L 50
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* C 100
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* D 500
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* M 1000
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*
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* Roman numerals are usually written from largest to smallest, from left to right.
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* There are six instances where this rule does not apply and subtraction is used instead:
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* I can be placed before V (5) and X (10) to make 4 (IV) and 9 (IX). (5 - 1 and 10 - 1, respectively)
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* X can be placed before L (50) and C (100) to make 40 (XL) and 90 (XC). (50 - 10 and 100 - 10, respectively)
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* C can be placed before D (500) and M (1000) to make 400 (CD) and 900 (CM). (500 - 100 and 1000 - 100, respectively)
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*
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* ----------------------------------------------------------------------------------------------------------------
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*
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* Examples:
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* 1) Input: s = "II"
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* Output: 2
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* Explanation: 2 = 1 + 1 = I + I.
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*
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* 2) Input: s = 31
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* Output: "XXXI"
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* Explanation: 31 = 30 + 1 = XXX + I.
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*
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* 3) Input: s = "CMXLI"
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* Output: 941
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* Explanation: 941 = 900 + 40 + 1 = CM + XL + I.
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*
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**/
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public class RomanNumeralConverter {
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/**
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* This method converts a roman numeral to its integer equivalent.
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* @param s The input roman numeral to be converted.
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* @return The integer equivalent of the roman numeral.
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*/
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public int romanToInt(String s){
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int result = 0;
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int prev = 0;
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// for each character in the given string
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for (int i = s.length() - 1; i >= 0; i--) {
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// get the integer value of the character
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int current = switch (s.charAt(i)) {
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case 'I' -> 1;
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case 'V' -> 5;
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case 'X' -> 10;
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case 'L' -> 50;
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case 'C' -> 100;
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case 'D' -> 500;
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case 'M' -> 1000;
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default -> throw new IllegalArgumentException("Invalid roman number");
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};
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// check if the right number is greater than the left number (previous character) in the given string (case of subtraction)
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if (current < prev) {
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result -= current; // subtract the right number from the result
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} else {
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result += current;
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}
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prev = current; // update the previous number
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}
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return result;
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}
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/**
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* This method converts an integer to its roman numeral equivalent.
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* @param num The input integer to be converted.
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* @return The roman numeral equivalent of the integer.
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*/
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public String intToRoman(int num) {
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// Create a hashmap to store the 7 basic roman numerals and the six special cases of subtraction
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HashMap<Integer, String> map = new HashMap<>();
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map.put(1,"I");
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map.put(4,"IV");
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map.put(5,"V");
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map.put(9,"IX");
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map.put(10,"X");
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map.put(40,"XL");
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map.put(50,"L");
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map.put(90,"XC");
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map.put(100,"C");
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map.put(400,"CD");
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map.put(500,"D");
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map.put(900,"CM");
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map.put(1000,"M");
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int[] arr = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1}; // store the keys of the hashmap in an array
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int len = arr.length;
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StringBuilder result = new StringBuilder();
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while(num > 0){
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int i;
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// find the largest number in the array that is less than or equal to the given number
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for(i = 0; i < len; i++) {
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if (arr[i] <= num) break;
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}
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result.append(map.get(arr[i])); // append the equivalent roman numeral to the result
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num = num - arr[i]; // subtract the found key from the given number
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}
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return result.toString();
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}
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public static void main(String[] args) {
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RomanNumeralConverter converter = new RomanNumeralConverter();
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// Roman to Integer
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System.out.println("Roman to Integer Conversion Examples:");
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System.out.println("DCXXI = " + converter.romanToInt("DCXXI"));
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System.out.println("II = " + converter.romanToInt("II"));
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System.out.println("CCXCIV = " + converter.romanToInt("CCXCIV"));
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System.out.println("IX = " + converter.romanToInt("IX"));
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System.out.println("XXXI = " + converter.romanToInt("XXXI"));
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System.out.println("CMXLI = " + converter.romanToInt("CMXLI"));
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System.out.println("MCCXXVI = " + converter.romanToInt("MCCXXVI"));
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System.out.println("CXLVIII = " + converter.romanToInt("CXLVIII"));
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System.out.println("<------------------------------------------------------------------->");
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// Integer to Roman
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System.out.println("Integer to Roman Conversion Examples:");
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System.out.println(621 + " = " + converter.intToRoman(621));
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System.out.println(2 + " = " + converter.intToRoman(2));
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System.out.println(294 + " = " + converter.intToRoman(294));
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System.out.println(9 + " = " + converter.intToRoman(9));
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System.out.println(31 + " = " + converter.intToRoman(31));
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System.out.println(941 + " = " + converter.intToRoman(941));
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System.out.println(1226 + " = " + converter.intToRoman(1226));
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System.out.println(148 + " = " + converter.intToRoman(148));
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}
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}
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@ -34,6 +34,7 @@
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- [Nth Geek Onacci Number](Maths/nth-geek-onacci-number.java)
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- [Random Node in Linked List](Maths/algorithms_random_node.java)
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- [Square Root using BinarySearch](Maths/square-root.java)
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- [Roman Numerals Conversion](Maths/roman-numerals.java)
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## Queues
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