Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

C++: #include <iostream>
using namespace std;

int main()
{
	int n, s = 0, rmin, imin;
	int a[100][100];
	int b[100];

	cin >> n;

	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> a[i][j];

	for (int i = 0; i < n; i++)
			b[i] = -1;

	b[0] = 0;
	int ct = 0;

	while (ct < n - 1) {
		imin = 0;
		rmin = 10000;
		for (int j = 0; j < n; j++) {
			if (b[j] > -1) {
				for (int i = 1; i < n; i++) {
					if (a[j][i] > -1 && b[i] < 0 && rmin > a[j][i]) {
						rmin = a[j][i];
						imin = i;
					}
				}
			}
		}
		b[imin] = rmin;
		ct++;
	}

	for (int i = 0; i < n; i++)
		s += b[i];

	cout << s << endl;

	return 0;
}

C++: #include<iostream>
using namespace std;

int n, M[100][100];

int prim(){
    int u, minv, d[100], p[100], c[100];
    
    for(int i = 0; i < n; i++){
        d[i] = (1<<21);
        p[i] = -1;
        c[i] = 0;
    }
    d[0] = 0;
    
    while(true){
        minv = (1<<21);
        u = -1;
        for(int i = 0; i < n; i++){
            if(minv > d[i] && c[i] != 2){
                u = i;
                minv = d[i];
            }
        }
        if(u == -1) break;
        c[u] = 2;
        for(int v = 0; v < n; v++){
            if(c[v] != 2 && M[u][v] != (1<<21)){
                if(d[v] > M[u][v]){
                    d[v] = M[u][v];
                    p[v] = u;
                    c[v] = 1;
                }
            }
        }
    }
    int sum = 0;
    for(int i = 0; i < n; i++){
        if(p[i] != -1) sum = sum + M[i][p[i]];
    }
    return sum;
}

int main(){
    cin >> n;
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            int e ;
            cin >> e;
            if(e == -1) M[i][j] = (1<<21);
            else M[i][j] = e;
        }
    }
    cout << prim() << endl;
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
static const int MAX=100;
static const int INFTY=(1<<21);
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,M[MAX][MAX];

int prim(){
	int u,minv;
	int d[MAX],p[MAX],color[MAX];
	for (int i = 0; i < n; ++i) {
		d[i]=INFTY;
		p[i]=-1;
		color[i]=WHITE;
	}
	d[0]=0;
	while(1){
		minv=INFTY;
		u=-1;
		for (int i = 0; i < n; ++i) {
			if (minv>d[i]&&color[i]!=BLACK) {
				u=i;
				minv=d[i];
			}
		}
		if(u==-1)break;
		color[u]=BLACK;
		for (int v = 0; v < n; ++v) {
			if(color[v]!=BLACK&&M[u][v]!=INFTY){
				if(d[v]>M[u][v]){
					d[v]=M[u][v];
					p[v]=u;
					color[v]=GRAY;
				}
			}
		}
	}
	int sum=0;
	for (int i = 0; i < n; ++i) {
		if(p[i]!=-1)sum+=M[i][p[i]];
	}
	return sum;
}



int main(){
	cin>>n;
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			int e;cin>>e;
			M[i][j]=(e==-1)?INFTY:e;
		}
	}
	cout<<prim()<<endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
#define MAX 100
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,d[MAX+10],p[MAX+10],color[MAX+10];
int W[MAX+10][MAX+10];

int prim()
{
  int v,k,mini,flag,u=0;
  for(int i=0;i<n;i++)
  {
      d[i]=INT_MAX;
      p[i]=-1;
  }
  d[0]=0;
  while(1)
  {
      mini=INT_MAX;
      flag=1;
      for(int i=0;i<n;i++)
      {
          if(d[i]<mini&&color[i]!=BLACK)
          {
              u=i;
              mini=d[i];
              flag=0;
          }
      }
      if(flag) break;
      color[u]=BLACK;
      for(v=0;v<n;v++)
      {
          if(W[u][v]!=INT_MAX&&color[v]!=BLACK)
          {
            if(d[v]>W[u][v])
            {
              d[v]=W[u][v];//更新当前点到最小生成树的距离
              p[v]=u;//每一轮都需要跑更新前驱结点
            }
          }
      }
  }
  int sum=0;
  for(int i=0;i<n;i++)
  {
      if(p[i]!=-1) sum+=W[i][p[i]];
  }
  return sum;
}

int main()
{
    cin>>n;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
         int e;
         cin>>e;
         W[i][j]=(e==-1)?INT_MAX:e;
        }
        color[i]=WHITE;
    }
    cout<<prim()<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;    using vvi = vector<vi>;
using vb = vector<bool>;   using vvb = vector<vb>;
using vl = vector<ll>;     using vvl = vector<vl>;
using vd = vector<double>; using vvd = vector<vd>;

#define REP(i,n) for(auto i = 0 * n; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()
#define FOR(i,s,e) for (ll i = s; i < (ll)e; i++)
#define TEN(x) ((ll)1e##x)

class UnionFind {
	typedef size_t U;
	vector<int32_t> v;
public:
	UnionFind(U n) : v(n, -1) {}
	U find(U x) { return v[x] < 0 ? x : (v[x] = find((U)v[x])); }
	bool same(U x, U y) { return find(x) == find(y); }
	U size(U x) { return (U)-v[find(x)]; }
	void unite(U x, U y) {
		x = find(x); y = find(y);
		if (x != y) {
			if (-v[x] < -v[y]) swap(x, y);
			v[x] += v[y];
			v[y] = x;
		}
	}
};

struct Edge{ uint32_t to, id; };
typedef vector<vector<Edge>> Graph;

template<class T> struct Kruskal{
	typedef uint32_t U;
	template<class V> Kruskal(U n, const V & u, const V & v, const vector<T> & w) : g(n) {
		vector<U> es(w.size());
		iota(es.begin(), es.end(), 0);
		sort(es.begin(), es.end(), [&](U i, U j) { return w[i] < w[j]; });
		UnionFind uf(n);
		for (U i : es) {
			if (!uf.same(u[i], v[i])) {
				uf.unite(u[i], v[i]); cost += w[i];
				g[u[i]].push_back(Edge{ v[i], i }); g[v[i]].push_back(Edge{ u[i], i });
			}
		}
	}
	Graph g; T cost = 0;
};

int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cout << fixed << setprecision(50);

	ll n; cin >> n;
	vl u, v, w;
	REP(i, n) REP(j, n) {
		ll x; cin >> x;
		if (x != -1) {
			u.push_back(i);
			v.push_back(j);
			w.push_back(x);
		}
	}
	Kruskal<ll> mst(n, u, v, w);
	cout << mst.cost << endl;
}