Beautiful Arrangement LeetCode solution in C++

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class Solution {
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 public:
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  int ans = 0;
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  bool isBeautiful(vector<int> &v) {
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    int i = v.size() - 1;
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    if (v[i] % (i + 1) == 0 || (i + 1) % v[i] == 0) return true;
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    return false;
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  }
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  void solve(int n, vector<int> &p, vector<bool> &seen) {
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    if (p.size() == n) {
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      ans++;
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      return;
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    }
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    for (int i = 1; i <= n; i++) {
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      if (seen[i]) continue;
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      p.push_back(i);
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      if (isBeautiful(p)) {
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        seen[i] = true;
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        solve(n, p, seen);
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        seen[i] = false;
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      }
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      p.pop_back();
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    }
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  }
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  int countArrangement(int n) {
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    vector<int> p;
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    vector<bool> seen(n + 1, false);
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    solve(n, p, seen);
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    return ans;
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  }
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};