# Roman to Integer LeetCode Solution | Easy Approach Share:

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 before `V` (5) and `X` (10) to make 4 and 9.
• `X` can be placed before `L` (50) and `C` (100) to make 40 and 90.
• `C` can be placed before `D` (500) and `M` (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]`.

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;

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]]

``````

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