13. Roman to Integer
Roman numerals are represented by seven different symbols:
For example, two is written as
II in Roman numeral, just two one’s added together. Twelve is written as,
XII, which is simply
II. The number twenty seven is written as
XXVII, which is
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:
Ican be placed before
X(10) to make 4 and 9.
Xcan be placed before
C(100) to make 40 and 90.
Ccan be placed before
M(1000) to make 400 and 900.
Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from
**- 时间复杂度: O(N)**- 空间复杂度: O(1)**