graph/kruskal.cpp

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• Last update: 2021-06-21 15:24:20+09:00

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template <typename T>
struct edge {
    int from, to;
    T cost;

    edge(int to, T cost) : from(-1), to(to), cost(cost) {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost) {}

    explicit operator int() const {return to;}
};

class UnionFind {
    vector<int> uni;
    int n;
public:
    explicit UnionFind(int n) : uni(static_cast<uint>(n), -1) , n(n){};

    int root(int a){
        if (uni[a] < 0) return a;
        else return (uni[a] = root(uni[a]));
    }

    bool unite(int a, int b) {
        a = root(a);
        b = root(b);
        if(a == b) return false;
        if(uni[a] > uni[b]) swap(a, b);
        uni[a] += uni[b];
        uni[b] = a;
        return true;
    }
};

template< typename T >
T kruskal(vector<edge<T>> &G, int V)
{
    sort(begin(G), end(G), [](const edge< T > &a, const edge< T > &b) { return (a.cost < b.cost); });
    UnionFind tree(V);
    T ret = 0;
    for(auto &e : G) {
        if(tree.unite(e.from, e.to)) ret += e.cost;
    }
    return (ret);
}

#line 1 "graph/kruskal.cpp"
template <typename T>
struct edge {
    int from, to;
    T cost;

    edge(int to, T cost) : from(-1), to(to), cost(cost) {}
    edge(int from, int to, T cost) : from(from), to(to), cost(cost) {}

    explicit operator int() const {return to;}
};

class UnionFind {
    vector<int> uni;
    int n;
public:
    explicit UnionFind(int n) : uni(static_cast<uint>(n), -1) , n(n){};

    int root(int a){
        if (uni[a] < 0) return a;
        else return (uni[a] = root(uni[a]));
    }

    bool unite(int a, int b) {
        a = root(a);
        b = root(b);
        if(a == b) return false;
        if(uni[a] > uni[b]) swap(a, b);
        uni[a] += uni[b];
        uni[b] = a;
        return true;
    }
};

template< typename T >
T kruskal(vector<edge<T>> &G, int V)
{
    sort(begin(G), end(G), [](const edge< T > &a, const edge< T > &b) { return (a.cost < b.cost); });
    UnionFind tree(V);
    T ret = 0;
    for(auto &e : G) {
        if(tree.unite(e.from, e.to)) ret += e.cost;
    }
    return (ret);
}

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