Go: package main

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

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

Python: N = int(input())
L = []  # input


def prim():
    # 頂点を適当に選ぶ
    s = None
    for i in range(N):
        for j in range(N):
            if L[i][j] != -1:
                s = i
                break
        if s is not None:
            break
    p = {s}
    T = []
    k = 0
    while k < N - 1:
        # 最終のP内で一番短いやつを加える
        len = float("inf")
        lenside = []
        for sg in p:
            for i in range(N):
                isT = False
                for t in T:
                    if (t[0] == sg and t[1] == i) or (t[0] == i and t[1] == sg):
                        # print("ignore")
                        isT = True
                        continue
                if isT is False and i not in p and L[sg][i] != -1 and L[sg][i] < len:
                    len = L[sg][i]
                    lenside = [sg, i]

        p.add(lenside[0])
        p.add(lenside[1])
        T.append(lenside)
        k = k + 1
        #print(p,T,k)
    cnt = 0
    for t in T:
        cnt += L[t[0]][t[1]]
    print(cnt)


for i in range(N):
    L.append(list(map(int, input().split())))
prim()

Python: import sys, collections
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = 10**10
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def same(self, x, y):
        return self.find(x) == self.find(y)

def kruskal(es, V):
    es.sort(key=lambda x:x[2])
    uf = UnionFind(V)
    res = 0
    for e in es:
        if not uf.same(e[0], e[1]):
            uf.unite(e[0], e[1])
            res += e[2]
    return res

def resolve():
    n = I()
    es = []
    for i in range(n):
        a = LI()
        for j in range(n):
            if a[j]!=-1:
                es.append((i, j, a[j]))

    ans = kruskal(es, n)
    print(ans)

if __name__ == '__main__':
    resolve()

Python: import heapq


def prim(adj):
    INF = 3000
    n = len(adj)
    state, d, p = [False] * n, [INF] * n, [-1] * n
    d[0] = 0
    pq = [(d[0], 0)]
    while pq:
        f, u = heapq.heappop(pq)
        state[u] = True
        if d[u] < f:
            continue
        for v, c in adj[u]:
            if state[v]:
                continue
            if c < d[v]:
                d[v] = c
                p[v] = u
                heapq.heappush(pq, (d[v], v))
    return d


def adj_matrix_to_list(matrix):
    n = len(matrix)
    li = [[] for _ in range(n)]
    for u in range(n):
        for v in range(n):
            if matrix[u][v] != -1:
                li[u].append((v, matrix[u][v]))
    return li


def main():
    n = int(input())
    m = [list(map(int, input().split())) for _ in range(n)]
    adj = adj_matrix_to_list(m)
    print(sum(prim(adj)))


if __name__ == '__main__':
    main()

Python: def main():
     def root(x):
          path=[]
          while x!=P[x]:
               path.append(x)
               x=P[x]
          for i in path:
               P[i]=x
          return x
     
     def is_same_set(x,y):
          return root(x)==root(y)
     
     def unite(x,y):
          P[root(x)]=root(y)
     
     n=int(input())
     P=[i for i in range(n)]
     edge_CostAndVertex=[]
     for i in range(n):
          cost=list(map(int,input().split()))
          for j in range(i):
               if cost[j]!=-1:
                    edge_CostAndVertex.append([cost[j],[i,j]])
                    
     edge_CostAndVertex.sort(key=lambda x:x[0])
     ans=0
     check=[]#連結されている頂点
     main_edge=edge_CostAndVertex[0][1][0]
     for i in edge_CostAndVertex:
          cost_i,a,b=i[0],i[1][0],i[1][1]
          if is_same_set(a,b):
               continue
          else:

               unite(a,b)
               ans+=cost_i
               if a not in check:
                    check.append(a)
               if b not in check:
                    check.append(b)
               if len(check)==n:
                    flag=1
                    for i in range(n):
                         for j in range(i):
                              if is_same_set(i,j):
                                   continue
                              else:
                                   flag=0
                                   break
                    if flag==1:
                         break
                    
     print(ans)
                    
if __name__=='__main__':
     main()