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: INF = 1e9

n = int(input())

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

def prim(n):
    flag = [0] * n
    d = [INF] * n
    d[0] = 0
    p = [-1] * n

    while True:
        min_cost = INF
        
        for i in range(n):
            if flag[i] != 1 and d[i] < min_cost:
                min_cost = d[i]
                u = i
        if min_cost == INF:
            break
        flag[u] = 1
        
        for v in range(n):
            if flag[v] != 1 and a[u][v] != -1:
                if a[u][v] < d[v]:
                    d[v] = a[u][v]
                    p[v] = u
    return sum(d)

print(prim(n))

Python: n=int(input())
# m=[list(map(int,input().split()))for _ in[0]*n]
m = [[-1 for i in range(n)] for j in range(n)]
d=[0]+[10**9]*n
b=[1]*n
a=0
while 1:
  u=-1
  for i in range(n):
    if b[i] and (u<0 or d[i]<d[u]):
      u=i
  if u<0:
    break
  b[u]=0
  a+=d[u]
  for v in range(n):
    t=m[u][v]
    if t+1 and d[v]>t:
      d[v]=t
print(a)

Python: import heapq

def make_adj_list(v):
    adj_list = [[-1 for i in range(v)] for j in range(v)]
    return adj_list

def prim(adj_list, v, s):
    # スタートを0とする
    min_d = 0
    heap = []
    used = []
    for i in range(v):
        used.append(False)
    used[s] = True
    for i in range(v):
        if adj_list[s][i] != -1:
            heapq.heappush(heap, (adj_list[s][i], i))
        #　スタートからつなぐことができる辺をheapに入れる

    while len(heap) != 0:
        cost, to = heapq.heappop(heap)
        if used[to]:
            continue
        min_d += cost
        used[to] = True
        for i in range(v):
            if adj_list[to][i] != -1:
                heapq.heappush(heap, (adj_list[to][i], i)) 
            #集合に入れた頂点からつなぐことができる辺をheapに入れる

    return min_d

def main():
    v = int(input())
    adj_list = make_adj_list(v)
    for i in range(v):
        adj_list[i] = [int(j) for j in input().split()]
    min_d = prim(adj_list, v, 0)
    print(min_d)

if __name__ == "__main__":
    main()

Python: class UnionFindTree:
    """
        Disjoint set data structure
        Union-Find tree
        complexity:
            init: O(n)
            find, unite, same: O(alpha(n))
    """
    def __init__(self, n):
        self.par = list(range(n))
        self.rank = [0] * n

    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def unite(self, x, y):
        x, y = self.find(x), self.find(y)
        if x == y:
            return
        elif self.rank[x] < self.rank[y]:
            self.par[x] = y
        else:
            self.par[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

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


class Kruskal:
    """
        Kruskal's algorithm: find Minimum Spanning Tree
        complexity:
            O(E logV)
    """
    def __init__(self, V, E, start=0, INF=10**9):
        """
        :param V: the number of vertices
        :param E:  adjacency list (undirected graph)
        :param start:
        :param INF:
        """
        self.kruskal(V, E)

    def kruskal(self, V, E):
        edges = []
        for v1 in range(V):
            for v2, cost in E[v1]:
                if v1 < v2:
                    edges.append((cost, v1, v2))
        edges.sort(reverse=True)
        self.mincost = 0
        self.min_spanning_tree = []
        uf = UnionFindTree(V)
        while len(self.min_spanning_tree) < V - 1:
            cost, v1, v2 = edges.pop()
            if not uf.same(v1, v2):
                self.mincost += cost
                uf.unite(v1, v2)
                self.min_spanning_tree.append((v1, v2, cost))

    def min_cost(self):
        return self.mincost

    def get_min_spanning_tree(self):
        return sorted(self.min_spanning_tree)


V = int(input())
edges = [[] for _ in range(V)]
for i in range(V):
    for j, d in enumerate(map(int, input().split())):
        if d != -1:
            edges[i].append((j, d))
mst = Kruskal(V, edges)
print(mst.min_cost())

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#!/usr/bin/env python
from __future__ import division, print_function
from sys import stdin, maxint
 
 
def main():
    num = int(stdin.readline())
 
    M = []
    for _ in xrange(num):
        M.append([int(s) for s in stdin.readline().split()])
 
    g = set(xrange(1, num+1))
    index = g.pop()
    h = {index}
    weight = 0
 
    while g:
        minimum = maxint
        for j in h:
            mj = M[j-1]
            for i in g:
                if 0 <= mj[i-1] < minimum:
                    index = i
                    minimum = mj[i-1]
        h.add(index)
        g.remove(index)
        weight += minimum
 
    print(weight)