Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

Python: # Minimum Spanning Tree

INF = 10**5
N, *W = map(int, open(0).read().split())
W = tuple(zip(*[iter(INF if w < 0 else w for w in W)]*N))

S = set([0])
ans = 0
while len(S) < N:
    min_w = INF
    u = -1
    for v in S:
        for j, w in enumerate(W[v]):
            if j not in S and w < min_w:
                min_w = w
                u = j

    ans += min_w
    S.add(u)
    
print(ans)

Python: def prim(cost):
    sumcost = 0
    V = len(cost)
    mincost = [float('inf')] * V
    used = [False] * V
    mincost[0] = 0
    while True:
        v = -1
        for u in range(V):
            if not used[u] and (v == -1 or mincost[u] < mincost[u]):
                v = u
        if v == -1: break
        used[v] = True
        sumcost = sumcost + mincost[v]
        for u in range(V):
            if cost[u][v] == -1:
                continue
            mincost[u] = min(mincost[u], cost[v][u])
    return sumcost

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))