Exclusive Time of Functions LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> exclusiveTime(int n, vector<string> &logs) {
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    vector<int> ret(n, 0);
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    stack<pair<int, int>> st;
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    for (auto &l : logs) {
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      auto p1 = l.find(':', 0), p2 = l.find(':', p1 + 1);
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      auto id = stoi(l.substr(0, p1));
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      auto time = stoi(l.substr(p2 + 1));
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      if (l[p1 + 1] == 's') {
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        st.push({id, time});
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      } else {
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        auto diff = time - st.top().second + 1;
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        ret[st.top().first] += diff;
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        st.pop();
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        if (!st.empty()) ret[st.top().first] -= diff;
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      }
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    }
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    return ret;
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  }
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};