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class Solution {
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 public:
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  int romanToInt(string s) {
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    unordered_map<char, int> T = {{'I', 1},   {'V', 5},   {'X', 10},  {'L', 50},
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                                  {'C', 100}, {'D', 500}, {'M', 1000}};
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    int sum = T[s.back()];
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    for (int i = s.length() - 2; i >= 0; --i) {
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      if (T[s[i]] < T[s[i + 1]])
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        sum -= T[s[i]];
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      else
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        sum += T[s[i]];
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    }
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    return sum;
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  }
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};