13. Roman to Integer (JAVA)
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: L = 50, V= 5, III = 3.
Example 5:
Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
class Solution {
public int romanToInt(String s) {
String sym = "MDCLXVI";
int[] val = {1000,500,100,50,10,5,1};
int num = 0;
int p; //array pointer
for(int i = 0; i < s.length(); i++){
p = sym.indexOf(s.charAt(i));
if(i+1 < s.length() && sym.indexOf(s.charAt(i+1)) < p){
num = num + val[sym.indexOf(s.charAt(i+1))] - val[p];
i++;
}
else{
num += val[p];
}
}
return num;
}
}
解题思路:要处理的一个特殊情况是4,9,40...这类数,所以我们要扫描到当前位之后的那一位,判断是不是这种情况,做相应处理。
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