Number of Visible People in a Queue LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> canSeePersonsCount(vector<int> &h) {
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    vector<int> ans;
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    stack<int> s;
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    int a = 0;
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    for (int i = h.size() - 1; i >= 0; i--) {
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      if (s.empty()) {
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        ans.push_back(a);
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        s.push(h[i]);
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        a++;
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      } else {
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        if (s.top() > h[i]) {
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          ans.push_back(1);
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          s.push(h[i]);
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          a++;
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        } else {
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          int b = 0;
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          while (!s.empty() && s.top() < h[i]) {
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            s.pop();
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            a--;
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            b++;
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          }
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          if (!s.empty()) b++;
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          ans.push_back(b);
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          s.push(h[i]);
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          a++;
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        }
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      }
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    }
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    reverse(ans.begin(), ans.end());
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    return ans;
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  }
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};