题目:
Roman numerals are represented by seven different symbols: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example, two is written as Roman numerals are usually written largest to smallest from left to right. However, the numeral for four is not
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. |
罗马数字包含以下七种字符: 字符 数值 I 1 V 5 X 10 L 50 C 100 D 500 M 1000 例如, 罗马数字 2 写做 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
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。 示例 1: 输入: "III" 输出: 3 示例 2: 输入: "IV" 输出: 4 示例 3: 输入: "IX" 输出: 9 示例 4: 输入: "LVIII" 输出: 58 解释: L = 50, V= 5, III = 3. 示例 5: 输入: "MCMXCIV" 输出: 1994 解释: M = 1000, CM = 900, XC = 90, IV = 4. |
思路:用哈希表 映射字符与对应的值,从前往后依次扫描。当从刚开始或者左边的字母大于等于右边的字符,则直接加上对应的数,否则i不为0且左边的字母小于右边的字母,则需要加上右边字母的值减去左边字母的值, 这里注意我们从前往后扫描,会多加一次较小值,所以在此多减去1个 较小的值,比如"IV",先ret=ret+1,然后V比I大,ret+=5-1,然后相当于多加了第一个1,再减去就可以了ret=4;
class Solution {
public:
int romanToInt(string s) {
int ret=0;
unordered_map<char,int> m{{'I',1},{'V',5},{'X',10},{'L',50},{'C',100},
{'D',500},{'M',1000}};
for(int i=0;i<s.size();++i)
{
if(i==0 || m[s[i]]<=m[s[i-1]]) ret += m[s[i]];
else ret += m[s[i]] - 2*m[s[i-1]];
}return ret;
}
};