LeetCode刷题（C++）——Roman to Integer（Easy）

Bertha 。 2022-06-16 01:50 163阅读 0赞

Given a roman numeral, convert it to an integer.

Input is guaranteed to be within the range from 1 to 3999.

1-9：\{ "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX" \}

10-90：\{ "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC" \}

100-900：\{ "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM" \}

1000-3000：\{ "M", "MM", "MMM" \}

<table style="border-spacing:0px; border-collapse:collapse; margin:5px 0px; word-wrap:break-word; word-break:break-all; line-height:22px; color:rgb(0,0,0); font-family:arial,宋体,sans-serif"> 
 <tbody> 
  <tr> 
   <th style="padding:2px 10px; height:23px; border:1px solid rgb(230,230,230); background-color:rgb(249,249,249)"> <span style="font-size:18px">基本字符</span></th> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">I</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">V</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">X</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">L</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">C</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">D</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">M</span> 
    </div> </td> 
  </tr> 
  <tr> 
   <th style="padding:2px 10px; height:23px; border:1px solid rgb(230,230,230); background-color:rgb(249,249,249)"> <span style="font-size:18px">相应的阿拉伯数字表示为</span></th> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">1</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">5</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">10</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">50</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">100</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">500</span> 
    </div> </td> 
   <td style="margin:0px; padding:2px 10px; height:22px; border:1px solid rgb(230,230,230)"> 
    <div style="word-wrap:break-word; color:rgb(51,51,51); margin:0px; line-height:24px; zoom:1; height:auto"> 
     <span style="font-size:18px">1000</span> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

相同的数字连写、所表示的数等于这些数字相加得到的数、如：Ⅲ=3；

小的数字在大的数字的右边、所表示的数等于这些数字相加得到的数、 如：Ⅷ=8、Ⅻ=12；

小的数字（限于 I、X 和 C）在大的数字的左边、所表示的数等于大数减小数得到的数、如：Ⅳ=4、Ⅸ=9；

正常使用时、连写的数字重复不得超过三次；

class Solution {
    public:
        int romanToInt(string s) {
            int ans = charToNum(s[0]);
    		for (int i = 1; i < s.size();i++)
    		{
    			if (charToNum(s[i - 1]) < charToNum(s[i]))
    				ans += charToNum(s[i]) - 2* charToNum(s[i - 1]);
    			else
    				ans += charToNum(s[i]);
    		}
    		return ans;
    	}
    
    	int charToNum(char x)
    	{
    		switch (x)
    		{
    		case 'I':
    			return 1;
    		case 'V':
    			return 5;
    		case 'X':
    			return 10;
    		case 'L':
    			return 50;
    		case 'C':
    			return 100;
    		case 'D':
    			return 500;
    		case 'M':
    			return 1000;
    		default:
    			break;
    		}
    		return 0;
        }
    };