All Ancestors of a Node in a Directed Acyclic Graph LeetCode solution in C++

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class Solution {
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 public:
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  void dfs(vector<vector<int>> &graph, int i, int j, vector<vector<int>> &ans, vector<bool> &vis) {
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    vis[j] = true;
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    for (auto &x : graph[j]) {
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      if (!vis[x]) {
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        ans[x].push_back(i);
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        dfs(graph, i, x, ans, vis);
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      }
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    }
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  }
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  vector<vector<int>> getAncestors(int n, vector<vector<int>> &edges) {
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    vector<vector<int>> ans(n), graph(n);
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    for (auto &v : edges) {
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      graph[v[0]].push_back(v[1]);
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    }
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    for (int i = 0; i < n; i++) {
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      vector<bool> vis(n);
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      dfs(graph, i, i, ans, vis);
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    }
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    return ans;
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  }
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};