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132 lines
3.2 KiB
Markdown
132 lines
3.2 KiB
Markdown
# [13. Roman to Integer](https://leetcode.com/problems/roman-to-integer/)
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## 题目
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Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`.
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```
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Symbol Value
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I 1
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V 5
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X 10
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L 50
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C 100
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D 500
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M 1000
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```
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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`.
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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:
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- `I` can be placed before `V` (5) and `X` (10) to make 4 and 9.
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- `X` can be placed before `L` (50) and `C` (100) to make 40 and 90.
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- `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900.
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Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999.
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**Example 1**:
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```
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Input: "III"
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Output: 3
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```
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**Example 2**:
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```
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Input: "IV"
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Output: 4
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```
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**Example 3**:
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```
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Input: "IX"
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Output: 9
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```
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**Example 4**:
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```
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Input: "LVIII"
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Output: 58
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Explanation: L = 50, V= 5, III = 3.
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```
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**Example 5**:
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```
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Input: "MCMXCIV"
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Output: 1994
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Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.
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```
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## 题目大意
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罗马数字包含以下七种字符: I， V， X， L，C，D 和 M。
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```go
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字符 数值
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I 1
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V 5
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X 10
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L 50
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C 100
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D 500
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M 1000
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```
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例如， 罗马数字 2 写做 II ，即为两个并列的 1。12 写做 XII ，即为 X + II 。 27 写做 XXVII, 即为 XX + V + II 。
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通常情况下，罗马数字中小的数字在大的数字的右边。但也存在特例，例如 4 不写做 IIII，而是 IV。数字 1 在数字 5 的左边，所表示的数等于大数 5 减小数 1 得到的数值 4 。同样地，数字 9 表示为 IX。这个特殊的规则只适用于以下六种情况：
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- I 可以放在 V (5) 和 X (10) 的左边，来表示 4 和 9。
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- X 可以放在 L (50) 和 C (100) 的左边，来表示 40 和 90。
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- C 可以放在 D (500) 和 M (1000) 的左边，来表示 400 和 900。
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给定一个罗马数字，将其转换成整数。输入确保在 1 到 3999 的范围内。
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## 解题思路
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- 给定一个罗马数字，将其转换成整数。输入确保在 1 到 3999 的范围内。
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- 简单题。按照题目中罗马数字的字符数值，计算出对应罗马数字的十进制数即可。
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## 代码
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```go
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package leetcode
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var roman = map[string]int{
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"I": 1,
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"V": 5,
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"X": 10,
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"L": 50,
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"C": 100,
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"D": 500,
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"M": 1000,
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}
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func romanToInt(s string) int {
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if s == "" {
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return 0
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}
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num, lastint, total := 0, 0, 0
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for i := 0; i < len(s); i++ {
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char := s[len(s)-(i+1) : len(s)-i]
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num = roman[char]
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if num < lastint {
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total = total - num
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} else {
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total = total + num
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}
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lastint = num
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}
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return total
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}
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``` |