description:
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.
Example 1:
Input: "III"
Output: 3
Example 2:
Input: "IV"
Output: 4
Example 3:
Input: "IX"
Output: 9
Example 4:
Input: "LVIII"
Output: 58
Explanation: C = 100, L = 50, XXX = 30 and III = 3.
Example 5:
Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4. -----------------------------------------------------------------------------
It is definitely not hard problem but hard to understand.
IV:4 XL:40 CD:400 !!!!!!!!!!!!
IX:9 XC:90 CM:900 !!!!!!!!!!!!
just determine the case of I, X, C
class Solution {
//pre store them first
public int romanToInt(String s) {
Map<Character, Integer> table = new HashMap<>();
table.put('I',1);table.put('V',5);table.put('X',10);table.put('L',50);table.put('C',100);table.put('D',500);table.put('M',1000);
//s is not null
//string operation
int res = 0;
for(int i = 0; i<s.length(); i++){
char ele = s.charAt(i);
if(ele == 'I' && i<s.length()-1){
i++;
char ele1 = s.charAt(i);
if(ele1=='V') res+=4;
else if(ele1 == 'X') res+=9;
else{
i--;
res+=table.get(ele);
}
}else if(ele == 'X' && i<s.length()-1){
i++;
char ele1 = s.charAt(i);
if(ele1=='L') res+=40;
else if(ele1 == 'C') res+=90;
else{
i--;
res+=table.get(ele);
}
}else if(ele == 'C' && i<s.length()-1){
i++;
char ele1 = s.charAt(i);
if(ele1=='D') res+=400;
else if(ele1 == 'M') res+=900;
else{
i--;
res+=table.get(ele);
}
}else {
res += table.get(ele);
}
}
return res;
}
}