LeetCode 2192. All Ancestors of a Node in a Directed Acyclic Graph

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class Solution {
public:
    vector<vector<int>> getAncestors(int n, vector<vector<int>>& edges) {
        vector<vector<int>> g(n), ans(n);
        for (auto &e : edges)
            g[e[0]].emplace_back(e[1]);
        function<void(int, int)> dfs = [&](int f, int u) {
            for (int v : g[u]) {
                if (ans[v].empty() || ans[v].back() != f) {
                    ans[v].emplace_back(f);
                    dfs(f, v);
                }
            }
        };
        for (int i = 0; i < n; ++i)
            dfs(i, i);
        return ans;
    }
}; 
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class Solution {
public:
    vector<vector<int>> getAncestors(int n, vector<vector<int>>& edges) {
        bitset<1000> a[1000];
        for (auto &e : edges)
            a[e[0]][e[1]] = 1;
        for (int v = 0; v < n; ++v)
            for (int u = 0; u < n; ++u)
                if (a[u][v])
                    a[u] |= a[v];
        vector<vector<int>> ans;
        for (int v = 0; v < n; ++v) {
            vector<int> f;
            for (int u = 0; u < n; ++u)
                if (a[u][v])
                    f.emplace_back(u);
            ans.emplace_back(f);
        }
        return ans;
    }
}; 
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class Solution {
public:
    vector<vector<int>> getAncestors(int n, vector<vector<int>>& edges) {
        vector<vector<int>> g(n), ans(n);
        vector<int> d(n);
        vector<set<int>> f(n);
        for (auto &e : edges) {
            g[e[0]].emplace_back(e[1]);
            ++d[e[1]];
        }
        queue<int> q;
        for (int i = 0; i < n; ++i)
            if (d[i] == 0)
                q.emplace(i);
        while (q.size()) {
            int u = q.front(); q.pop();
            for (int v : g[u]) {
                f[v].insert(u);
                f[v].insert(f[u].begin(), f[u].end());
                if (--d[v] == 0) {
                    q.emplace(v);
                }
            }
        }
        for (int i = 0; i < n; ++i)
            ans[i].assign(f[i].begin(), f[i].end());
        return ans;
    }
};