Roman Numeral to Integer - Amazon Top Interview Questions

Problem Statement :

Given a string numeral representing a Roman numeral, convert it to an integer.

Roman numerals contain the symbols representing values in the following list:

"I" = 1
"V" = 5
"X" = 10
"L" = 50
"C" = 100
"D" = 500
"M" = 1000

Roman numerals are typically written largest to smallest, from left to right, and can be computed by summing up the values of all the symbols. However, in some cases, when a symbol of lower value is to the left of a symbol of higher value, then the lower value is subtracted from the higher one.

There are 6 cases where this is possible:

When "I" is before "V", we get 4.
When "I" is before "X", we get 9.
When "X" is before "L", we get 40.
When "X" is before "C", we get 90.
When "C" is before "D", we get 400.
When "C" is before "M", we get 900.


1 ≤ n ≤ 15 where n is the length of numeral

1 ≤ k ≤ 3000 where k is the number numeral represents

Example 1


numeral = "XII"




"XII" = 10 + 1 + 1 = 12

Example 2


numeral = "XIV"




"XIV" = 10 + 4 = 14

Solution :


                        Solution in C++ :

int solve(string numeral) {
    unordered_map<char, int> mp;
    mp['I'] = 1;
    mp['V'] = 5;
    mp['X'] = 10;
    mp['L'] = 50;
    mp['C'] = 100;
    mp['D'] = 500;
    mp['M'] = 1000;

    int n = numeral.length();

    int prev = INT_MAX;
    int curr;
    int ans = 0;

    for (int i = 0; i < n; i++) {
        curr = mp[numeral[i]];  // get the current value
        ans += curr;            // add it to result
        if (curr > prev) {      // subtractive case
            ans -= 2 * prev;
        prev = curr;  // update prev for next iteration

    return ans;

                        Solution in Python : 
class Solution:
    def solve(self, numeral):
        value = {"M": 1000, "D": 500, "C": 100, "L": 50, "X": 10, "V": 5, "I": 1}
        res = 0
        prev = 0
        for i in range(len(numeral) - 1, -1, -1):
            n = value[numeral[i]]
            if n >= prev:
                res += int(n)
                res -= int(n)
            prev = n
        return res

View More Similar Problems

Pair Sums

Given an array, we define its value to be the value obtained by following these instructions: Write down all pairs of numbers from this array. Compute the product of each pair. Find the sum of all the products. For example, for a given array, for a given array [7,2 ,-1 ,2 ] Note that ( 7 , 2 ) is listed twice, one for each occurrence of 2. Given an array of integers, find the largest v

View Solution →

Lazy White Falcon

White Falcon just solved the data structure problem below using heavy-light decomposition. Can you help her find a new solution that doesn't require implementing any fancy techniques? There are 2 types of query operations that can be performed on a tree: 1 u x: Assign x as the value of node u. 2 u v: Print the sum of the node values in the unique path from node u to node v. Given a tree wi

View Solution →

Ticket to Ride

Simon received the board game Ticket to Ride as a birthday present. After playing it with his friends, he decides to come up with a strategy for the game. There are n cities on the map and n - 1 road plans. Each road plan consists of the following: Two cities which can be directly connected by a road. The length of the proposed road. The entire road plan is designed in such a way that if o

View Solution →

Heavy Light White Falcon

Our lazy white falcon finally decided to learn heavy-light decomposition. Her teacher gave an assignment for her to practice this new technique. Please help her by solving this problem. You are given a tree with N nodes and each node's value is initially 0. The problem asks you to operate the following two types of queries: "1 u x" assign x to the value of the node . "2 u v" print the maxim

View Solution →

Number Game on a Tree

Andy and Lily love playing games with numbers and trees. Today they have a tree consisting of n nodes and n -1 edges. Each edge i has an integer weight, wi. Before the game starts, Andy chooses an unordered pair of distinct nodes, ( u , v ), and uses all the edge weights present on the unique path from node u to node v to construct a list of numbers. For example, in the diagram below, Andy

View Solution →

Heavy Light 2 White Falcon

White Falcon was amazed by what she can do with heavy-light decomposition on trees. As a resut, she wants to improve her expertise on heavy-light decomposition. Her teacher gave her an another assignment which requires path updates. As always, White Falcon needs your help with the assignment. You are given a tree with N nodes and each node's value Vi is initially 0. Let's denote the path fr

View Solution →