Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX   = 100
	INFTY = (1 << 21)
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

//V: グラフの頂点全体の集合
//T: MSTに属する頂点の集合
var (
	n     int
	M     [MAX][MAX]int //重みを記録する隣接行列
	color [MAX]int
	p     [MAX]int //MSTにおける頂点の親を記録
	d     [MAX]int //Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを記録
)

func prim() int {
	var u, minv int
	//初期化
	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}

	d[0] = 0

	for {
		//頂点uを決めていく
		//つまり、Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを決める
		minv = INFTY
		u = -1
		for i := 0; i < n; i++ {
			//未訪問かつ、辺の重みが最小となるuを選ぶ
			if minv > d[i] && color[i] != BLACK {
				u = i
				minv = d[i]
			}
		}

		if u == -1 {
			break
		}

		color[u] = BLACK
		for v := 0; v < n; v++ {
			//未訪問かつ、辺が存在するとき
			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
				}
			}
		}
	}

	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {

		for j := 0; j < n; j++ {
			tmp := nextInt()
			if tmp == -1 {
				tmp = INFTY
			}
			M[i][j] = tmp
		}

	}

	fmt.Println(prim())

}

C++: #include<iostream>
#include<list>
#include<vector>
const int INF = 2001;
using namespace std;
list<int> L;
bool ok(int i) {
    for (list<int>::iterator it = L.begin(); it != L.end(); it++) if (i == *it) return 0;
    return 1;
}
int main() {
    L.push_back(0);
    int n; cin >> n;
    int M[100][100];
    int tmp = INF;
    int id = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> M[i][j];
            if (i == 0 && M[i][j] != -1) {
                if (M[i][j] < tmp) {
                    tmp = M[i][j];
                    id = j;
                }
            }
        }
    }
    L.push_back(id);
    int ans = tmp;
    tmp = INF;
    int OK[100];
    while (1) {
        tmp = INF;
        for (int i = 0; i < n; i++) OK[i] = ok(i); //reached?
        for (list<int>::iterator it = L.begin(); it != L.end(); it++ ) { //from reached
            for (int i = 0; i < n; i++) {
                if (M[*it][i] < tmp && M[*it][i] != -1 && OK[i]) {
                    tmp = M[*it][i];
                    id = i;
                }
            }
        }
        if (tmp == INF) break;
        ans += tmp;
        L.push_back(id);
    }
    cout << ans << endl;
    return 0;
    
}