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, two is written as II
in Roman numeral, just two one's added together. Twelve is written as, XII
, which is simply X
+ II
. The number twenty seven 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. Input is guaranteed to be within the range from 1 to 3999.
class Solution { public: int romanToInt(string s) { int ans = 0; int n = s.length(); map<int, int> mp; mp['I'] = 1; mp['V'] = 5; mp['X'] = 10; mp['L'] = 50; mp['C'] = 100; mp['D'] = 500; mp['M'] = 1000; for (int i = 0; i < n; i++) { if (s[i] == 'I' && i + 1 < n) { if (s[i + 1] == 'V') { ans += 4; i++; continue; } else if (s[i + 1] == 'X') { ans += 9; i++; continue; } } else if (s[i] == 'X' && i + 1 < n) { if (s[i + 1] == 'L') { ans += 40; i++; continue; } else if (s[i + 1] == 'C') { ans += 90; i++; continue; } } else if (s[i] == 'C' && i + 1 < n) { if (s[i + 1] == 'D') { ans += 400; i++; continue; } else if (s[i + 1] == 'M') { ans += 900; i++; continue; } } ans += mp[s[i]]; } return ans; } };