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Convert a Roman Number to Decimal using Hashmap in Java
• Last Updated : 27 Aug, 2020

Given a Roman numeral, the task is to find the corresponding decimal value.

Note: Roman numerals are represented by seven different symbols: I, V, X, L, C, D, and M.

Examples:

Input: “III”

Output: 3

Input: “MDCCLX”

Output: 1760

Approach:

1. Loop through each character in the string containing the Roman numerals.
2. Compare the value of the current roman symbol with the value of the roman symbol to its right. If the current value is greater than or equal to the value of the symbol to the right, add the current symbol’s value to the total. If the current value is smaller than the value of the symbol to the right, subtract the current symbol’s value from the total.

Below is the implementation of the above approach:

## Java

 `// Java Program to Convert a Roman``// Number to Decimal using Hashmap``import` `java.io.*;``import` `java.util.Scanner;``import` `java.util.HashMap;``class` `solution {``    ``int` `romanToInt(String s)``    ``{``        ``// Create a empty hash map.``        ``HashMap map = ``new` `HashMap<>();`` ` `        ``// Putting value in hash map.``        ``map.put(``'I'``, ``1``);``        ``map.put(``'V'``, ``5``);``        ``map.put(``'X'``, ``10``);``        ``map.put(``'L'``, ``50``);``        ``map.put(``'C'``, ``100``);``        ``map.put(``'D'``, ``500``);``        ``map.put(``'M'``, ``1000``);`` ` `        ``// Creating integer variable to store result.``        ``int` `result = ``0``;`` ` `        ``// initialize loop to iterate in string.``        ``for` `(``int` `i = ``0``; i < s.length(); i++) {`` ` `            ``// Checking that current element``            ``// is not smaller then previous``            ``if` `(i > ``0``                ``&& map.get(s.charAt(i))``                       ``> map.get(s.charAt(i - ``1``))) {``                ``result += map.get(s.charAt(i))``                          ``- ``2` `* map.get(s.charAt(i - ``1``));``            ``}``            ``else` `{``                ``result += map.get(s.charAt(i));``            ``}``        ``}``        ``// Returning the integer value of Roman number.``        ``return` `result;``    ``}``}``public` `class` `GFG {`` ` `    ``public` `static` `void` `main(String[] args)``    ``{``        ``String s;``       ` `        ``// Scanner sc = new Scanner(System.in);``        ``// s = sc.nextLine();``        ``solution gfg = ``new` `solution();``        ``System.out.println(gfg.romanToInt(``"MDCCLX"``));``    ``}``}`

Output:

`1760`

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