# Leetcode #13. Roman to integer

Https://leetcode.com/problems/roman-to-integer/description/

 

Roman numerals are represented by seven different symbols:I,V,X,L,C,DAndM.

Symbol       ValueI             1V             5X             10L             50C             100D             500M             1000

For example, two is writtenIIIn Roman numeral, just two one's added together. Twelve is written,XII, Which is simplyX+II. The number twenty seven is writtenXXVII, Which isXX+V+II.

Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is notIIII. Instead, the number four is writtenIV. Because the one is before the five we subtract it making four. The same principle applies to the number nine, which is writtenIX. There are six instances where Subtraction is used:

• ICan be placed beforeV(5) andX(10) To make 4 and 9.
• XCan be placed beforeL(50) andC(100) to make 40 and 90.
• CCan be placed beforeD(500) andM(1000) to make 400 and 900.

Given a roman numeral, convert it to an integer. input is guaranteed to be within the range from 1 to 3999.

Example 1:

Input: "III"Output: 3

Example 2:

Input: "IV"Output: 4

Example 3:

Input: "IX"Output: 9

Example 4:

Input: "LVIII"Output: 58Explanation: L = 50, V= 5, III = 3.

Example 5:

Input: "MCMXCIV"Output: 1994Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

Code:

class Solution {public:    int romanToInt(string s) {        int val[10] = {1, 5, 10, 50, 100, 500, 1000};        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 len = s.length();        int ans = mp[s[len - 1]];        int cnt = mp[s[len - 1]];        for(int i = len - 2; i >= 0; i --) {            if(mp[s[i]] < cnt)                ans = ans - mp[s[i]];            else ans += mp[s[i]];            cnt = mp[s[i]];        }        return ans;    }};

　　

# Leetcode #13. Roman to integer