String - 13. Roman to Integer
13. 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, 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
思路:
对于I V X C可以观察出规律,如果之前累积的结果大于它们后面进位的大写字母,就不符合规则,返回负一否则继续累加。
代码:
java:
class Solution {
public static int romanToInt(String s) {
int res = 0;
for (int i = s.length() - 1; i >= 0; i--) {
char c = s.charAt(i);
switch (c) {
case 'I':
res += (res >= 5 ? -1 : 1);
break;
case 'V':
res += 5;
break;
case 'X':
res += 10 * (res >= 50 ? -1 : 1);
break;
case 'L':
res += 50;
break;
case 'C':
res += 100 * (res >= 500 ? -1 : 1);
break;
case 'D':
res += 500;
break;
case 'M':
res += 1000;
break;
}
}
return res;
}
}
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