13. Roman to Integer

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Given a roman numeral, convert it to an integer.

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

class Solution {public:    int romanToInt(string s) {        int cnt = 0;        int n = s.size();        for(int i = 0; i < n - 1; i++)        {            if(tonumber(s[i]) < tonumber(s[i+1]))            cnt -= tonumber(s[i]);            else            cnt += tonumber(s[i]);                    }        cnt += tonumber(s[n - 1]);        return cnt;            }        int tonumber(char ch)    {        switch(ch)        {            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: return 0;          }        return 0;    }};

better answer map的用法写的太精巧。，

int romanToInt(string s)  {        static unordered_map<char, int> ROMAN = {{'I', 1}, {'V', 5}, {'X', 10}, {'L', 50}, {'C', 100}, {'D', 500}, {'M', 1000},};        int value = 0;        for (int i = 0; i < s.size(); i++) value += ((i < s.size() - 1 && ROMAN[s[i+1]] > ROMAN[s[i]]) ? -ROMAN[s[i]] : ROMAN[s[i]]);        return value;    }

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