Go: package main

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

const (
	MAX_N      = 200
	MAX_WEIGHT = 2000
)

type Edge struct {
	start  int
	end    int
	weight int
}

type ShortestInfo struct {
	edges    []Edge
	shortest int
}

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

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

	shortestList := make([]ShortestInfo, n)
	for i := 1; i < n; i++ {
		shortestList[i] = ShortestInfo{edges: []Edge{}, shortest: MAX_N*MAX_WEIGHT + 1}
	}

	adjacentMatrix := make([][]int, n)
	for i := 0; i < n; i++ {
		adjacentMatrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			v, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjacentMatrix[i][j] = v
		}
	}

	mst([]int{1}, shortestList, adjacentMatrix)
	fmt.Println(shortestList)
	fmt.Println(calculateMinWeight(shortestList))
}

func calculateMinWeight(shortestList []ShortestInfo) int {
	visitedList := make([]bool, len(shortestList))
	visitedList[0] = true
	sumWeight := 0
	for !visitedAll(visitedList) {
		shortestInfo := shortestList[0]
		shortestList = shortestList[1:]
		edges := shortestInfo.edges
		for _, edge := range edges {
			if !visitedList[edge.end-1] {
				visitedList[edge.end-1] = true
				sumWeight += edge.weight
			}
		}
	}
	return sumWeight
}

func visitedAll(visitedList []bool) bool {
	for _, v := range visitedList {
		if !v {
			return false
		}
	}
	return true
}

func mst(nodeStack []int, shortestList []ShortestInfo, adjacentMatrix [][]int) {
	for len(nodeStack) > 0 {
		currentNode := nodeStack[0]
		nodeStack = nodeStack[1:]
		currentShortest := getShortest(currentNode, shortestList)
		adjacents := findAdjacents(currentNode, adjacentMatrix)
		for i := 0; i < len(adjacents); i++ {
			adj := adjacents[i]
			s := getShortest(adj.end, shortestList)
			if currentShortest.shortest+adj.weight < s.shortest || (currentShortest.shortest+adj.weight == s.shortest && len(currentShortest.edges)+1 > len(s.edges)) {
				setShortest(adj.end, adj, currentShortest, shortestList)
				nodeStack = append(nodeStack, adj.end)
			}
		}
	}
}

func getShortest(node int, shortestList []ShortestInfo) ShortestInfo {
	return shortestList[node-1]
}

func setShortest(node int, edge Edge, currentShortest ShortestInfo, shortestList []ShortestInfo) {
	newEdges := make([]Edge, len(currentShortest.edges)+1)
	for i := 0; i < len(newEdges)-1; i++ {
		newEdges[i] = currentShortest.edges[i]
	}
	newEdges[len(newEdges)-1] = edge
	shortestInfo := ShortestInfo{edges: newEdges, shortest: currentShortest.shortest + edge.weight}
	shortestList[node-1] = shortestInfo
}

func findAdjacents(currentNode int, adjacentMatrix [][]int) []Edge {
	adjacents := adjacentMatrix[currentNode-1]
	edges := []Edge{}
	for i, v := range adjacents {
		if v > 0 {
			edges = append(edges, Edge{start: currentNode, end: i + 1, weight: v})
		}
	}
	return edges
}

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

Python: #coding:utf-8
inf = 1000000
n = int(input())
mtrx = []
for i in range(n):
    nums = list(map(int,input().split()))
    col = []
    for j in range(n):
        if nums[j] == -1:
            col.append(inf)
        else:
            col.append(nums[j])
    mtrx.append(col)

        
d = [inf for i in range(n)]
p = [-1 for i in range(n)]
color = ["white" for i in range(n)]
d[0] = 0
while True:
    mincost = inf
    for i in range(n):
        if color[i] != "black" and d[i] < mincost:
            mincost = d[i]
            u = i
    if mincost == inf:
        break

    color[u] = "black"
    for v in range(n):
        if color[v] != "black" and mtrx[u][v] < inf:
            if mtrx[u][v] < d[v]:
                d[v] = mtrx[u][v]
                p[v] = u
                color[v] = "gray"
print(sum(d))

Python: n = int(input())
sides = []
ws = []
ss = []
for _ in range(n):
    sides.append(list(map(int,input().split())))
for i in range(n):
    for j in range(i+1,n):
        if sides[i][j] >= 0:
            ws.append([sides[i][j],i,j])
rs = [(i) for i in range(n)]
def root(x):
    global rs
    if rs[x] == x:
        return(x)
    else:
        return(root(rs[x]))
ws.sort()
ans = 0
while(len(ws)):
    if root(ws[0][1]) != root(ws[0][2]):
        ans += ws[0][0]
        rs[root(rs[ws[0][2]])] = root(ws[0][1])
        ss.append(ws[0])
    del(ws[0])
print(ans)

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: # -*- coding: utf-8 -*-
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 as adjacency matrix
    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

    # sample input when given not as adjacency matrix
    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
    '''

    n = len(edges)
    mst = []
    cost = 0
    T = [start]

    while True:
        tmp_edges = [(cost, (u, v)) for u in T for v, cost in enumerate(edges[u]) if cost != default_value and v not in T] if adj_matrix else\
                    [(cost, (u, v)) for u in T for v, cost in edges[u] if v not in T]

        if tmp_edges:
            min_cost, min_edge = min(tmp_edges)
            mst.append(min_edge)
            cost += min_cost
            T.append(min_edge[1])

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

            else:
                return mst, cost


class NoSpanningError(Exception):
    pass


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

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

    print(prim(edges, adj_matrix=True)[1])