Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

Python: INFTY = 1 << 21
WHITE = 0
GRAY = 1
BLACK = 2

def prim(n, m):
    d = [INFTY] * n
    p = [-1] * n
    color = [WHITE] * n

    d[0] = 0

    while True:
        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

    w_sum = 0
    for i in range(n):
        if p[i] != -1:
            w_sum += m[i][p[i]]

    return w_sum


n = int(input())
m = []
for i in range(n):
    line = [int(v) for v in input().split()]
    for j in range(n):
        if line[j] == -1:
            line[j] = INFTY
    m.append(line)

print(prim(n, m))

Python: import heapq

n = int(input())
A = [[int(i) for i in input().split()] for i in range(n)]
h = []
DP = {}
heapq.heappush(h,(0,0))
c = 0
while(True):
    tmp = heapq.heappop(h)
    if tmp[1] in DP:
        continue
    c += tmp[0]
    DP[tmp[1]] = 1
    if len(DP) == n:
        break
    for i,j in enumerate(A[tmp[1]]):
        if j > 0 and not i in DP:
            heapq.heappush(h,(j,i))
print(c)

Python: # -*- coding: utf-8 -*-

import sys

sys.setrecursionlimit(10 ** 9)
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
INF=float('inf')

# Union-Find木
class UnionFind:
    def __init__(self, n):
        self.n = n
        # 親要素のノード番号を格納。par[x] == xの時そのノードは根
        # 1-indexedのままでOK、その場合は[0]は未使用
        self.par = [i for i in range(n+1)]
        # 木の高さを格納する（初期状態では0）
        self.rank = [0] * (n+1)
        # あるノードを根とする集合に属するノード数
        self.size = [1] * (n+1)
        # あるノードを根とする集合が木かどうか
        self.tree = [True] * (n+1)

    # 根の検索(グループ番号と言えなくもない)
    def find(self, x):
        # 根ならその番号を返す
        if self.par[x] == x:
            return x
        else:
            # 走査していく過程で親を書き換える
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    # 併合
    def union(self, x, y):
        # 根を探す
        x = self.find(x)
        y = self.find(y)

        # 木かどうかの判定用
        if x == y:
            self.tree[x] = False
            return
        if not self.tree[x] or not self.tree[y]:
            self.tree[x] = self.tree[y] = False

        # 木の高さを比較し、低いほうから高いほうに辺を張る
        if self.rank[x] < self.rank[y]:
            self.par[x] = y
            self.size[y] += self.size[x]
        else:
            self.par[y] = x
            self.size[x] += self.size[y]
            # 木の高さが同じなら片方を1増やす
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # 同じ集合に属するか判定
    def same(self, x, y):
        return self.find(x) == self.find(y)

    # あるノードの属する集合のノード数
    def get_size(self, x):
        return self.size[self.find(x)]

    # 木かどうかの判定
    def is_tree(self, x):
        return self.tree[self.find(x)]

    # 集合の数
    def len(self):
        res = set()
        for i in range(self.n+1):
            res.add(self.find(i))
        # グループ0の分を引いて返却
        return len(res) - 1

N=INT()
G=[[None] for i in range(N)]
for i in range(N):
    G[i]=LIST()

# 隣接行列を辺集合(cost, u, v)にする
edges=[]
for i in range(N):
    for j in range(i+1, N):
        if G[i][j]!=-1:
            edges.append((G[i][j], i, j))

# クラスカル法
edges.sort()
uf=UnionFind(N)
ans=0
for cost, u, v in edges:
    if not uf.same(u, v):
        uf.union(u, v)
        ans+=cost
print(ans)

Python: # -*- coding: utf-8 -*-
from collections import deque


class Graph:
    def __init__(self, n, adj_matrix, default_value=float('inf')):
        self.n = n
        self.adj_matrix = adj_matrix
        self.default_value = default_value

    def show(self):
        for _ in self.adj_matrix:
            print(*_)

    def set_mst(self, start=0):  # minimum spanning tree
        self.mst = []
        T = [start]

        for _ in range(self.n - 1):
            edges = [(cost, u, v) for u in T
                     for v, cost in enumerate(self.adj_matrix[u])
                     if cost != self.default_value and v not in T]

            min_cost, *min_edge = min(edges)
            self.mst.append(tuple(min_edge))
            T.append(min_edge[1])

    def show_mst(self):
        self.set_mst()
        print(sum([self.adj_matrix[u][v] for u, v in self.mst]))

    def dfs(self):
        self.states = [2] * self.n
        self.d = [None] * self.n
        self.f = [None] * self.n
        self.time = 0

        for u in range(self.n):
            if self.states[u] == 2:
                self.dfs_visit(u)

    def dfs_visit(self, u):
        self.states[u] = 1
        self.time += 1
        self.d[u] = self.time

        for v, edge in [(v, edge) for v, edge in enumerate(self.adj_matrix[u])
                        if edge]:
            if self.states[v] == 2:
                self.dfs_visit(v)

        self.states[u] = 0
        self.time += 1
        self.f[u] = self.time

    def show_dfs(self, start=0):
        self.dfs()
        for i, (d, f) in enumerate(zip(self.d, self.f)):
            print(i + 1, d, f)

    def bfs(self, start):
        self.states = [0] * self.n
        self.dists = [float('inf')] * self.n

        queue = deque([start])
        self.dists[start] = 0
        while queue:
            u = queue.popleft()
            edges = self.adj_matrix[u]

            for v, edge in [(v, edge) for v, edge in enumerate(edges) if edge]:
                if self.states[v]:
                    continue

                if self.dists[v] > self.dists[u] + 1:
                    self.dists[v] = self.dists[u] + 1
                queue.append(v)

                self.states[v] = 1

        self.dists = [
            -1 if dist == float('inf') else dist for dist in self.dists
        ]

    def show_bfs(self, start=0):
        self.bfs(start=start)
        for i, dist in enumerate(self.dists):
            print(i + 1, dist)


if __name__ == '__main__':
    n = int(input())
    adj_matrix = [[
        int(cost) if int(cost) != -1 else float('inf')
        for cost in input().split()
    ] for i in range(n)]

    g = Graph(n, adj_matrix)
    g.show_mst()