PAT : 数据结构与算法题目集（中文）7-10 公路村村通

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#include <iostream>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
int UnionF[1001];
struct Heapstruct
{
    int head, tail, value;
};
bool Compare(const Heapstruct &a, const Heapstruct &b)
{
    return a.value > b.value;
}
int getdigit(void)
{
    int temp{0};
    while (1)
    {
        char ch = getchar();
        if (ch == ' ' || ch == '\n' || ch == EOF)
            return temp;
        temp = temp * 10 + ch - '0';
    }
}
int GetFind(const int num)
{
    if (UnionF[num] <= -1)
        return num;
    UnionF[num] = GetFind(UnionF[num]);
    return UnionF[num];
}
bool Find(const int &a, const int &b)
{
    int qa = GetFind(a);
    int qb = GetFind(b);
    if (qa != qb)
    {
        if (UnionF[qa] < UnionF[qb])
            UnionF[qb] = qa;
        else if (UnionF[qb] > UnionF[qa])
            UnionF[qa] = qb;
        else
        {
            --UnionF[qb];
            UnionF[qa] = qb;
        }
        return true;
    }
    return false;
}
int main(int argc, char *argv[])
{
    int N{getdigit()}, M{getdigit()}, SumValue{0}, EdgeAcc{0};
    fill(begin(UnionF), end(UnionF), -1);
    vector<Heapstruct> T(M);
    for (int i = 0; i < M; ++i)
    {
        T[i].head = getdigit();
        T[i].tail = getdigit();
        T[i].value = getdigit();
    }
    make_heap(T.begin(), T.end(), Compare);
    while (EdgeAcc != N-1 && !T.empty())
    {
        Heapstruct temp{T[0]};
        pop_heap(T.begin(), T.end(), Compare);
        T.pop_back();
        if (Find(temp.head, temp.tail))
        {
            SumValue += temp.value;
            ++EdgeAcc;
        }
    }
    if (T.empty())
        printf("-1\n");
    else
    printf("%d\n", SumValue);
    return EXIT_SUCCESS;
}

考虑到题目中说边数最多为顶点数的三倍，采用 Kruskal 算法，并查集（路径压缩+按高度合并）维护连通性。

 

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