13. Roman to Integer

最新推荐文章于 2024-01-03 14:43:50 发布

annjeff

最新推荐文章于 2024-01-03 14:43:50 发布

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分类专栏： LeetCode 文章标签：字符串处理罗马数字转阿拉伯数字 LeetCode

本文链接：https://blog.youkuaiyun.com/annjeff/article/details/88556828

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本文详细介绍了一种将罗马数字转换为整数的算法实现，包括特殊规则处理和实例解析，如IV转换为4，MCMXCIV转换为1994等。通过逐字符扫描并比较相邻字符值，实现了从1到3999范围内的罗马数字准确转换。

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13. Roman to Integer

1. Problem Description

2.My Solution

1. Problem Description

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 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:

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.

2.My Solution

class Solution {
public:
    int romanToInt(string s) {
        const int len = s.length();
        char str2arr[len+1] = { 0 };
        int index = 0;
        int total = 0;
        strcpy(str2arr, s.c_str());
        while (index < len)
        {
            switch (str2arr[index])
            {
            case 'C':
                if (str2arr[index + 1] == 'M')
                {
                    total += 900;
                    index += 2;
                    break;
                }
                else if (str2arr[index + 1] == 'D')
                {
                    total += 400;
                    index += 2;
                    break;
                }
                else
                {
                    total += 100;
                    index += 1;
                    break;
                }
            case 'X':
                if (str2arr[index + 1] == 'C')
                {
                    total += 90;
                    index += 2;
                    break;
                }
                else if (str2arr[index + 1] == 'L')
                {
                    total += 40;
                    index += 2;
                    break;
                }
                else
                {
                    total += 10;
                    index += 1;
                    break;
                }
            case 'I':
                if (str2arr[index + 1] == 'X')
                {
                    total += 9;
                    index += 2;
                    break;
                }
                else if (str2arr[index + 1] == 'V')
                {
                    total += 4;
                    index += 2;
                    break;
                }
                else
                {
                    total += 1;
                    index += 1;
                    break;
                }
            case 'M':
                total += 1000;
                index += 1;
                break;
            case 'D':
                total += 500;
                index += 1;
                break;
            case 'L':
                total += 50;
                index += 1;
                break;
            case 'V':
                total += 5;
                index += 1;
                break;
            default:
                break;

		}
	}
	return total;
}

};