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())

}

Python: a=input()
matrix=[]
for i in range(int(a)):
	matrix.append(list(map(int,input().split())))

# ?????????O(n)????????£?????????
class union_find(object):
 	"""union-find tree"""
 	def __init__(self, length):
 		self.length = length
 		self.unionnumber=0
 		self.unionlist=[[]]
 		self.num=list(-1 for i in range(length))

 	def unite(self,i,j):
 		if self.num[i]==-1:
 			if self.num[j]==-1:
 				self.unionlist[self.unionnumber].extend([i,j])
 				self.num[i]=self.unionnumber
 				self.num[j]=self.unionnumber
 				self.unionnumber+=1
 				self.unionlist.append([])
 			else:
 				tmp=i 
 				i=j 
 				j=tmp 
 		if self.num[i]!=-1:
 			if self.num[j]!=-1:
 				if self.num[i]==self.num[j]:
 					pass
 				else:
 					self.unionlist[self.num[i]].extend(self.unionlist[self.num[j]])
 					tmp=self.num[j]
 					for k in self.unionlist[self.num[j]]:
 						self.num[k]=self.num[i]
 					self.unionlist[tmp]="del"
 			else:
 				self.num[j]=self.num[i]
 				self.unionlist[self.num[i]].append(j)

 	def same(self,i,j):
 		if self.num[i]==-1 or self.num[j]==-1:
 			return(False)
 		else:
 			return(self.num[i]==self.num[j])

# ?????????=-1
def Kruskal(matrix):
	length=len(matrix)
	edgelist=[]
	for i in range(length):
		for j in range(i+1):
			if matrix[i][j]!=-1:
				edgelist.append([j,i,matrix[i][j]])
	edgelist.sort(key=lambda x:x[2],reverse=True)
	result=[[-1 for i in range(length)] for j in range(length)]
	union=union_find(length)
	while(edgelist!=[]):
		edge=edgelist.pop()
		i,j,score=edge
		if union.same(i,j):
			pass
		else:
			union.unite(i,j)
			result[i][j]=score
			result[j][i]=score
		
	return(result)

a=Kruskal(matrix)
count=0
for i in range(len(a)):
	for j in range(i):
		if a[i][j]!=-1:
			count+=a[i][j]

print(count)

Python: INF = 1e9

n = int(input())
adj_matrix = [list(map(int, input().split())) for i in range(n)]


def prim(x):
    isVisited = [False] * x
    d = [INF] * x 
    d[0] = 0
    p = [-1] * x 
    
    while True:
        min_cost = INF
        
        for i in range(x):
            if isVisited[i] != True and d[i] < min_cost:
                min_cost = d[i]
                u = i
        
        if min_cost == INF:
            break
        
        isVisited[u] = True
        
        for v in range(x):
            if isVisited[v] != True and adj_matrix[u][v] != -1:
                if adj_matrix[u][v] < d[v]:
                    d[v] = adj_matrix[u][v]
                    p[v] = u
    return sum(d)

print(prim(n))

Python: n = int(input())
m = []

for _ in range(n):
    tmp = [int(x) for x in input().split()]
    m.append(tmp)

#辺を全て持つリストを作る
edge_list = [] 
j = 1
for i in range(n-1):
    for k,x in enumerate(m[i][j:]):
        if x != -1:
            edge_list.append((x,i,k+j))
        else:
            pass
    j += 1
edge_list.sort()

root_list = [i for i in range(n)]

def root(x):
    path_to_root = []
    while root_list[x] != x:
        path_to_root.append(x)
        x = root_list[x]
    for node in path_to_root:
        root_list[node] = x
    return x

def is_same_root(x,y):
    return root(x) == root(y)

def unite(x,y):
    root_list[root(x)] = root(y)

cost = 0
for x in edge_list:
    w,p,q = x
    if is_same_root(p,q):
        continue
    else:
        cost += w
        unite(p,q)

print(cost)

Python: inf = float("inf")
class Node():

    def __init__(self, _id):
        self.id = _id
        self.d = inf
        self.pi = None
        self.color = 0
    
    def input_data(self):
        data = [int(i) for i in input().split()]
        self.adj = {G[i]: d
                    for i, d in enumerate(data)
                    if d != -1}
    
    def __hash__(self):
        return hash(self.id)
        
    

def prim():
    G[0].d = 0
    while True:
        mincost = inf
        for i in G:
            if i.color != 1 and i.d < mincost:
                mincost = i.d
                u = i
        
        if mincost == inf:
            break

        u.color = 1
        for v in u.adj.keys():
            if v.color != 1 and u.adj[v] < v.d:
                v.pi = u.id
                v.d = u.adj[v]

if __name__ == "__main__":
    n = int(input())
    G = [Node(i) for i in range(n)]
    [i.input_data() for i in G]
    prim()
    print(sum(g.d for g in G))

Python: n = int(input())
inf = float('inf')
graphs = []

for i in range(n):
    weights = list(map(int, input().split()))
    weights = [inf if weight == -1 else weight for weight in weights]
    graphs.append(weights)
# print(graphs)
# M =graphs
color = ['WHITE' for _ in range(n)]
d = [inf for _ in range(n)]
p = [i for i in range(n)]


def prim():
    d[0] = 0
    p[0] = -1
    while True:
        min_cost = inf
        for i in range(n):
            if color[i] != 'BLACK' and d[i] < min_cost:
                min_cost = d[i]
                u = i
        if min_cost == inf:
            break
        color[u] = 'BLACK'

        for v in range(n):
            if color[v] != 'BLACK' and graphs[u][v] != inf:
                if graphs[u][v] < d[v]:
                    d[v] = graphs[u][v]
                    p[v] = u
                    color[v] = 'GRAY'


prim()
# print(d)
# print(p)
print(sum(d))