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: n = int(input())
edge = []
for i in range(n):
    a = list(map(int, input().split()))
    for j in range(i + 1, n):
        if a[j] != -1:
            edge.append((a[j], i, j))
edge.sort()
ans = 0

tree = [i for i in range(n)]
def root(x):
    pre = []
    while x != tree[x]:
        pre.append(x)
        x = tree[x]
    for node in pre:
        tree[node] = x
    return x
def unite(x, y):
    X, Y = root(x), root(y)
    if X != Y:
        tree[X] = Y

for cost, x, y in edge:
    X, Y = root(x), root(y)
    if X != Y:
        ans += cost
        tree[X] = Y
print(ans)

Python: import sys
input = sys.stdin.readline
from operator import itemgetter
sys.setrecursionlimit(10000000)
INF = 10**30
M = []

def prim(G, root, n):
    BLACK = 1<<10
    WHITE = 1<<20
    nodes = [WHITE] * n
    d = [INF] * n
    d[root] = 0
    p = [0] * n
    p[root] = -1
    while True:
        mincost = INF

        # 探索
        for i in range(n):
            if d[i] < mincost and nodes[i] == WHITE:
                mincost = d[i]
                next = i
        if mincost == INF:
            break
        # 移動
        nodes[next] = BLACK

        # 伝播
        for i in range(n):
            if nodes[i] == WHITE and G[next][i] != INF:
                if G[next][i] < d[i]:
                    d[i] = G[next][i]
                    p[i] = next
    return d

def main():
    global M
    n = int(input().strip())
    M = [[0] * n for _ in range(n)]
    for i in range(n):
        M[i] = list(map(lambda x: INF if x == -1 else x, map(int, input().strip().split())))
    d = prim(M, 0, n)
    print(sum(d))

if __name__ == '__main__':
    main()

Python: # -*- coding: utf-8 -*-
from heapq import heappop, heappush


def prim(edges, *, start=0, adj_matrix=False, default_value=float('inf')):
    '''
    Returns the Minimum Spanning Tree(MST) of a given graph

    # sample input when given not as adjacency list (adj_matrix=False) (generally works faster)
    edges = [[(1, 2), (2, 5), (3, 4)],         # node 0
             [(0, 2), (3, 3), (4, 6)],         # node 1
             [(0, 5), (3, 2), (5, 6)],         # node 2
             [(0, 4), (1, 3), (2, 2), (4, 2)], # node 3
             [(1, 6), (3, 2), (5, 4)],         # node 4
             [(2, 6), (4, 4)]]                 # node 5

    # sample input when given as adjacency matrix (adj_matrix=True)
    edges = [[0, 2, 5, 4, inf, inf],           # node 0
             [2, 0, inf, 3, 6, inf],           # node 1
             [5, inf, 0, 2, inf, 6],           # node 2
             [4, 3, 2, 0, 2, inf],             # node 3
             [inf, 6, inf, 2, 0, 4],           # node 4
             [inf, inf, 6, inf, 4, 0]]         # node 5
    '''

    n = len(edges)

    costs = [float('inf')] * n
    costs[start] = 0
    prevs = [-1] * n

    pq = [(0, start)]
    T = [True] * n

    while pq:
        tmp_cost, tmp_node = heappop(pq)
        T[tmp_node] = False

        nxt_edges = ((node, cost) for node, cost in enumerate(edges[tmp_node]) if cost != default_value and T[node]) if adj_matrix else\
                    ((node, cost) for node, cost in edges[tmp_node] if T[node])

        for nxt_node, nxt_cost in nxt_edges:
            if costs[nxt_node] > nxt_cost:
                costs[nxt_node] = nxt_cost
                prevs[nxt_node] = tmp_node
                heappush(pq, (nxt_cost, nxt_node))
                T[nxt_node] = True

    else:
        if len([prev for prev in prevs if prev != -1]) != n - 1:
            raise NoSpanningError(
                'There is no spanning tree in this graph (search started from node{})'.
                format(start))

        else:
            return prevs, costs


class NoSpanningError(Exception):
    pass


if __name__ == '__main__':
    '''
    an example of using this function
    AIZU ONLINE JUDGE - ALDS_1_12_A
    '''

    n = int(input())
    edges = [[(j, int(cost)) for j, cost in enumerate(input().split())
              if int(cost) != -1] for i in range(n)]

    prevs, costs = prim(edges)
    print(sum(costs))

Python: import sys

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

def solve():
    n = int(input())
    edges = []

    for i in range(n):
        line = [int(j) for j in input().split()]
        edges += [e for e in line[i + 1:] if e >= 0]

    edges.sort()
    ans = sum(edges[:n - 1])

    print(ans)

if __name__ == '__main__':
    solve()

Python: n=int(input())
edgeList=[]
for i in range(n):
 a=list(map(int,input().split()))
 for j in range(i):
  if a[j]>0:edgeList+=[[a[j],i,j]]
rootList=[-1]*n
sumLength=0
def getRoot(x):
 r=rootList[x]
 if r<0:rootList[x]=x
 elif r!=x:rootList[x]=getRoot(r)
 return rootList[x]
edgeList.sort(key=lambda x:x[0])
for e in edgeList:
 x=getRoot(e[1])
 y=getRoot(e[2])
 if x!=y:
  sumLength+=e[0]
  rootList[x]=rootList[y]=min(x,y)
print(sumLength)

Python: from sys import stdin
INF = 1<<21
WHITE = 0
GRAY = 1
BLACK = 2
n = int(stdin.readline())
M = [[INF] * (n + 1) for _ in range(n + 1)]
for i in range(0, n):
    for j, e in enumerate(list(map(int, stdin.readline().split()))):
        if e != -1: M[i][j] = e
d = [INF] * n
d[0] = 0
t = [-1] * n
color = [0] * n
def prim():
    while True:
        minv = INF
        u = -1
        for i in range(0, 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(0, n):
            if color[v] != BLACK and d[v] > M[u][v]:
                d[v] = M[u][v]
                t[v] = u
                color[v] = GRAY
    return sum(d)
print(prim())