Roman to Integer | Roman numerals are represented by seven different symbols: I
, V
, X
, L
, C
, D
and M
.
Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000
For example, 2
is written as II
in Roman numeral, just two one’s added together. 12
is written as XII
, which is simply X + II
. The number 27
is written as XXVII
, which is XX + V + II
.
Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not IIII
. Instead, the number four is written as IV
. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is written as IX
. There are six instances where subtraction is used:
I
can be placed beforeV
(5) andX
(10) to make 4 and 9.X
can be placed beforeL
(50) andC
(100) to make 40 and 90.C
can be placed beforeD
(500) andM
(1000) to make 400 and 900.
Given a roman numeral, convert it to an integer.
Example 1:
Input: s = "III" Output: 3 Explanation: III = 3.
Example 2:
Input: s = "LVIII" Output: 58 Explanation: L = 50, V= 5, III = 3.
Example 3:
Input: s = "MCMXCIV" Output: 1994 Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
Constraints:
1 <= s.length <= 15
s
contains only the characters('I', 'V', 'X', 'L', 'C', 'D', 'M')
.- It is guaranteed that
s
is a valid roman numeral in the range[1, 3999]
.
Roman to Integer Solutions
✅Time: O(n)
✅Space: O(1)
C++
class Solution {
public:
int romanToInt(string s) {
int ans = 0;
vector<int> roman(128);
roman['I'] = 1;
roman['V'] = 5;
roman['X'] = 10;
roman['L'] = 50;
roman['C'] = 100;
roman['D'] = 500;
roman['M'] = 1000;
for (int i = 0; i + 1 < s.length(); ++i)
if (roman[s[i]] < roman[s[i + 1]])
ans -= roman[s[i]];
else
ans += roman[s[i]];
return ans + roman[s.back()];
}
};
Java
class Solution {
public int romanToInt(String s) {
int ans = 0;
int[] roman = new int[128];
roman['I'] = 1;
roman['V'] = 5;
roman['X'] = 10;
roman['L'] = 50;
roman['C'] = 100;
roman['D'] = 500;
roman['M'] = 1000;
for (int i = 0; i + 1 < s.length(); ++i)
if (roman[s.charAt(i)] < roman[s.charAt(i + 1)])
ans -= roman[s.charAt(i)];
else
ans += roman[s.charAt(i)];
return ans + roman[s.charAt(s.length() - 1)];
}
}
Python
class Solution:
def romanToInt(self, s: str) -> int:
ans = 0
roman = {'I': 1, 'V': 5, 'X': 10, 'L': 50,
'C': 100, 'D': 500, 'M': 1000}
for a, b in zip(s, s[1:]):
if roman[a] < roman[b]:
ans -= roman[a]
else:
ans += roman[a]
return ans + roman[s[-1]]
Watch Tutorial
Checkout more Solutions here