Lexicographical Numbers LeetCode solution in C++

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class Solution {
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 private:
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  void dfs(int i, int n, vector<int> &ans) {
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    if (i > n) return;
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    ans.push_back(i);
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    for (int j = 0; j < 10; ++j) dfs(i * 10 + j, n, ans);
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  }
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 public:
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  vector<int> lexicalOrder(int n) {
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    vector<int> ans;
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    for (int i = 1; i < 10; ++i) dfs(i, n, ans);
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    return ans;
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  }
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};