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LeetCode 13 - Roman to Integer

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问题描述

Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M.

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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:

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Input: "III"
Output: 3

Example 2:

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Input: "IV"
Output: 4

Example 3:

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Input: "IX"
Output: 9

Example 4:

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Input: "LVIII"
Output: 58
Explanation: C = 100, L = 50, XXX = 30 and III = 3.

Example 5:

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Input: "MCMXCIV"
Output: 1994
Explanation: M = 1000, CM = 900, XC = 90 and IV = 4.

Related Topics: Math, String

原问题: 13. Roman to Integer

中文翻译版: 13. 罗马数字转整数

解决方案

题目难度不大，根据题目描述可以写出代码

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#include <iostream>
#include <string>
using namespace std;

class Solution {
public:
    int romanToInt(string s)
    {
        int num = 0;
        int j;
        char ch;

        for (int i=0; i<s.size(); i++) {
            ch = s[i];
            j = i + 1;
            switch (ch) {
                case 'I':   // value 1
                    if (j < s.size() && (s[j] == 'V' || s[j] == 'X'))
                        num -= 1;
                    else
                        num += 1;
                    break;
                case 'V':   // value 5
                    num += 5;
                    break;
                case 'X':   // value 10
                    if (j < s.size() && (s[j] == 'L' || s[j] == 'C'))
                        num -= 10;
                    else
                        num += 10;
                    break;
                case 'L':   // value 50
                    num += 50;
                    break;
                case 'C':   // value 100
                    if (j < s.size() && (s[j] == 'D' || s[j] == 'M'))
                        num -= 100;
                    else
                        num += 100;
                    break;
                case 'D':   // value 500
                    num += 500;
                    break;
                case 'M':   // value 1000
                    num += 1000;
                    break;
            }
        }

        return num;
    }
};

int main()
{
    Solution solu;
    string str1 = "MCMXCIV";

    cout << str1 << ": " << solu.romanToInt(str1) << endl;

    return 0;
}