Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

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

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

Python: #!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys

WHITE, GRAY, BLACK = 0, 1, 2


def prim_span_tree():
    min_weight_vertices[0] = 0

    while True:
        min_cost = 2001
        current_vertex = -1
        for i in range(vertices_num):
            if color[i] != BLACK and min_weight_vertices[i] < min_cost:
                min_cost = min_weight_vertices[i]
                current_vertex = i

        if min_cost == 2001:
            break

        color[current_vertex] = BLACK

        for j in range(vertices_num):
            v_weight = int(init_vertices_matrix[current_vertex][j])
            if color[j] != BLACK and v_weight >= 0:
                if v_weight < min_weight_vertices[j]:
                    min_weight_vertices[j] = v_weight
                    parent_list[j] = current_vertex
                    color[j] = GRAY

    return min_weight_vertices


if __name__ == '__main__':
    _input = sys.stdin.readlines()
    vertices_num = int(_input[0])
    init_vertices_matrix = list(map(lambda x: x.split(), _input[1:]))

    parent_list, min_weight_vertices = [-1] * vertices_num, [2001] * vertices_num
    color = [WHITE] * vertices_num
    ans = prim_span_tree()
    print(sum(ans))

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

n = int(raw_input())
A = [0] * n
for i in range(n):
    A[i] = map(int, raw_input().split())

result = prim(A)
print(result)

Python: INFTY = 1 << 21
WHITE = 0
GRAY = 1
BLACK = 2
d = [INFTY for i in range(n)]
p = [-1 for i in range(n)]
color = [WHITE for i in range(n)]

n = int(input())
M = [list(map(int, input().split())) for i in range(n)]
for i in range(n):
    for j in range(n):
        if (M[i][j] == -1):
            M[i][j] = INFTY

def prim():
    global M, d, p, color
    d[0] = 0
    while(1):
        minv = INFTY
        u = -1
        for i in range(n):
            if (minv > d[i] and color[i] != BLACK):
                u = i
                minv = d[i]
        if (u == -1):
            break
        color[u] = BLACK
        for v in range(n):
            if (color[v] != BLACK and M[u][v] != INFTY):
                if (d[v] > M[u][v]):
                    d[v] = M[u][v]
                    p[v] = u
                    color[v] = GRAY
    
    return sum([M[i][p[i]] for i in range(n) if (p[i] != -1)])

print(prim())

Python: def root(x):
    path = []
    while P[x] != x:
        path.append(x)
        x = P[x]
    for node in path:
        P[node] = x
    return x
def check(x,y):
    if root(x) == root(y):
        return 1
    else:
        return 0
def unite(x,y):
    P[root(x)] = root(y)        

n = int(input())
P = [i for i in range(n)]
omomi = []
for k in range(n):
    s = list(map(int,input().split()))
    for l in range(n):
        if s[l] != -1:
            omomi.append([s[l],k,l])
omomi.sort()
ans = 0
for yee in range(len(omomi)):
    if check(omomi[yee][1],omomi[yee][2]) == False:
            unite(omomi[yee][1],omomi[yee][2])
            ans+=omomi[yee][0]
print(ans)

Python: from heapq import heappush, heappop, heapify

n = int(input())
g = [[] for _ in range(n)]

for i in range(n):
    for j,k in enumerate(map(int,input().split())):
        if k != -1:
            g[i].append((j,k))
#    print(g[i])

ocupied = [0]*n
que = [(j,k) for k,j in g[0]] # 重み、子の順番
#print(f'g[0]: {g[0]}')　#子、重みの順番
#print(f'que: {que}')
ocupied[0] = 1
heapify(que)

ans = 0
while que:
    cv,v = heappop(que)
    #print(f'cv, v: {cv}, {v}')
    if ocupied[v]: # vは頂点　どこでvが頂点になるか
        continue
    ocupied[v] = 1
    ans += cv
    for j,k in g[v]:
        if ocupied[j]:
            continue
        heappush(que,(k,j))
    #print(f'ocupied: {ocupied}')
print(ans)