Destination City LeetCode solution in C++

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class Solution {
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 public:
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  string destCity(vector<vector<string>> &paths) {
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    string ans;
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    unordered_map<string, int> m;
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    for (int i = 0; i < paths.size(); i++) {
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      m[paths[i][0]]++;
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      m[paths[i][1]]--;
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    }
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    for (auto city : m) {
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      if (city.second == -1) ans = city.first;
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    }
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    return ans;
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  }
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};