LeetCode-013：Roman to Integer

最新推荐文章于 2022-05-05 16:31:36 发布

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最新推荐文章于 2022-05-05 16:31:36 发布

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分类专栏： LeetCode 文章标签：打表模拟

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本文介绍了一种将罗马数字转换为整数的算法实现，通过解析罗马数字的特殊规则，如IV表示4而非简单的I+V，文章提供了一个C++代码示例，展示了如何通过遍历字符串并应用减法规则来正确计算罗马数字的值。

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题目：

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.

题意：

将给定罗马数字转变成阿拉伯数字

思路：

打表，模拟

Code：

class Solution {
public:
    int romanToInt(string s) {
        int val[127],i,y=0,len=s.length();
        val['I']=1;val['V']=5;val['X']=10;val['L']=50;
        val['C']=100;val['D']=500;val['M']=1000;
        for(i=0;i<len;i++){
            if(i&&val[s[i]]>val[s[i-1]]) y+=val[s[i]]-2*val[s[i-1]];
            else y+=val[s[i]];
        }
        return y;
    }
};