https://ac.nowcoder.com/acm/contest/330/G

C++版本一

题解：

std

最小生成树

看成一张图，就是把同类元素的试剂当作一个点之后，求这个图的最小生成树。
然后用你最喜欢的求MST的算法求解就好。注意判不连通的情况。

#include <bits/stdc++.h>
using namespace std;
 
int main()
{
    int n, m ,k;
    cin >> n >> m >> k;
    vector<int> a(n);
    for (auto& t : a) cin >> t, --t;
    vector<int> fa(k);
    iota(fa.begin(), fa.end(), 0);
    function<int(int)> find = [&](int x) { return fa[x] == x ? x : fa[x] = find(fa[x]); };
    auto unite = [&](int u, int v) { fa[find(u)] = find(v); };
    vector<tuple<int, int, int>> edges;
    for (int i = 0, u, v, c; i < m; i++)
    {
        cin >> u >> v >> c;
        --u, --v;
        edges.emplace_back(c, a[u], a[v]);
    }
    sort(edges.begin(), edges.end());
    long long ans = 0;
    int cnt = 0;
    int c, u, v;
    for (auto& e : edges)
    {
        tie(c, u, v) = e;
        if (find(u) == find(v)) continue;
        unite(u, v);
        ans += c;
        if (++cnt == k - 1) break;
    }
    if (cnt == k - 1)
        cout << ans << endl;
    else
        cout << -1 << endl;
}

扫一扫，把题目装进口袋

C++版本二

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=200000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q,x,y,c;
ll ans,cnt,flag,temp;
int a[N];
int pre[N];
char str;
struct node{
    int x,y,c;
    bool operator<(const node&S)const{
        return c<S.c;
    }
}e[N];
int find(int x){
    if(x==pre[x])
        return x;
    return pre[x]=find(pre[x]);
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d%d%d",&n,&m,&k);
    //scanf("%d",&t);
    //while(t--){}
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&x,&y,&e[i].c);
        e[i].x=a[x];
        e[i].y=a[y];
    }
    sort(e+1,e+m+1);
    for(int i=1;i<=k;i++)
        pre[i]=i;
    for(int i=1;i<=m;i++){
        int fx=find(e[i].x);
        int fy=find(e[i].y);
        if(fx!=fy){
            pre[fx]=fy;
            ans+=e[i].c;
        }
    }
    for(int i=1;i<=k;i++)
        if(pre[i]==i)
            cnt++;
    if(cnt==1)
        cout << ans << endl;
    else
        cout<<-1<<endl;

    //cout << "Hello world!" << endl;
    return 0;
}