LeetCode 1489. Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree

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class UF {
public:
    vector<int> f;
    vector<int> size;
    int n;
    int setCount; // count of current connected components
    UF(int _n): n(_n), setCount(_n), f(_n), size(_n, 1) {
        iota(f.begin(), f.end(), 0);
    }
    int find(int x) {
        return f[x] == x ? x : f[x] = find(f[x]);
    }
    bool _union(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y)
            return false;
        if (size[x] < size[y]) {
            swap(x, y);
        }
        f[y] = x;
        size[x] += size[y];
        --setCount;
        return true;
    }
    bool connected(int x, int y) {
        x = find(x);
        y = find(y);
        return x == y;
    }
};
class Solution {
public:
    vector<vector<int>> findCriticalAndPseudoCriticalEdges(int n, vector<vector<int>>& edges) {
        const int m = edges.size();
        for (int i = 0; i < m; ++i)
            edges[i].push_back(i); // preserve index before sorting
        sort(edges.begin(), edges.end(), [](const auto& u, const auto& v) {
            return u[2] < v[2]; // sort by weight
        });
        UF uf_std(n);
        int value = 0; // weight of MST
        for (int i = 0; i < m; ++i)
            if (uf_std._union(edges[i][0], edges[i][1]))
                value += edges[i][2];
        vector<vector<int>> ans(2);
        for (int i = 0; i < m; ++i) {
            UF uf(n);
            int v = 0;
            for (int j = 0; j < m; ++j)
                if (i != j && uf._union(edges[j][0], edges[j][1])) // without the i-th edge
                    v += edges[j][2];
            if (uf.setCount != 1 // graph can't be conncted as a single component
                || (uf.setCount == 1 && v > value)) { // or can be a conncted component with larger weight
                ans[0].push_back(edges[i][3]); // critical edges
                continue;
            }
            uf = UF(n);
            uf._union(edges[i][0], edges[i][1]);
            v = edges[i][2];
            for (int j = 0; j < m; ++j)
                if (i != j && uf._union(edges[j][0], edges[j][1]))
                    v += edges[j][2];
            if (v == value)
                ans[1].push_back(edges[i][3]); // pseudo-critical edges
        }
        return ans;
    }
};