Number of Squareful Arrays LeetCode solution in C++

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class Solution {
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 public:
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  int numSquarefulPerms(vector<int> &nums) {
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    sort(nums.begin(), nums.end());
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    int ans = 0;
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    solve(nums, 0, ans);
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    return ans;
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  }
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  void solve(vector<int> nums, int idx, int &ans) {
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    if (idx >= nums.size()) {
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      ++ans;
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    }
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    for (int i = idx; i < nums.size(); i++) {
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      if (i > idx && nums[i] == nums[idx]) continue;
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      swap(nums[i], nums[idx]);
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      if (idx == 0 || (idx > 0 && isSquare(nums[idx] + nums[idx - 1]))) solve(nums, idx + 1, ans);
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    }
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  }
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  bool isSquare(int n) {
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    int temp = sqrt(n);
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    return temp * temp == n;
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  }
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};