# 0013._Roman_To_Integer

# 13. Roman to Integer

**难度: Easy**

## 刷题内容

原题连接

内容描述

Roman numerals are represented by seven different symbols: `I`

, `V`

, `X`

, `L`

, `C`

, `D`

and `M`

.

1 | Symbol Value |

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 before`V`

(5) and`X`

(10) to make 4 and 9.`X`

can be placed before`L`

(50) and`C`

(100) to make 40 and 90.`C`

can be placed before`D`

(500) and`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 `1`

to `3999`

.

##### Example 1:

1 | Input: "III" |

##### Example 2:

1 | Input: "IV" |

##### Example 3:

1 | Input: "IX" |

##### Example 4:

1 | Input: "LVIII" |

##### Example 5:

1 | Input: "MCMXCIV" |

## 解题方案

******- 时间复杂度: O(N)******- 空间复杂度: O(1)******

代码：

1 | /** |