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: from __future__ import division, print_function
from sys import stdin, maxint
 
 
def main():
    num = int(stdin.readline())
 
    y = []
    for _ in xrange(num):
        it = iter(int(s) for s in stdin.readline().split()[1:])
        y.append([(next(it), next(it)) for _ in xrange(next(it))])
    weight = [maxint] * num
    weight[0] = 0
    t = set(xrange(1, num))
    index = 0
 
    while t:
        for v, cost in y[index]:
            if v not in t:
                continue
            weight[v] = min(weight[v], cost + weight[index])

        index = min(t, key=lambda i: weight[i])
        t.remove(index)

    for i, d in enumerate(weight):
        print(i, d)
 
 
main()

Python: # coding: utf-8

n = int(input())
ew = [None] * n
for i in range(n):
    ew[i] = list(map(int, input().split()))

elist = []
for i in range(n):
    for j in range(i+1, n):
        if ew[i][j] > -1:
            elist.append((ew[i][j], i, j))


class UnionFind(object):
    def __init__(self, n):
        self.parent = [i for i in range(n)]

    def find_root(self, i):
        if self.parent[i] != i:
            p = self.parent[i]
            self.parent[i] = self.find_root(p)
        return self.parent[i]

    def same_group(self, i, j):
        return self.find_root(i) == self.find_root(j)

    def union(self, i, j):
        i = self.find_root(i)
        j = self.find_root(j)
        if i != j:
            self.parent[j] = i


uf = UnionFind(n)
esum = 0
for edge in sorted(elist):
    if not uf.same_group(edge[1], edge[2]):
        uf.union(edge[1], edge[2])
        esum += edge[0]

print(esum)

Python: # -*- coding: utf-8 -*-
"""
Created on Sat Apr  6 18:01:32 2019

@author: Yamazaki Kenichi
"""

n = int(input())
A = [list(map(int,input().split())) for i in range(n)]
INFTY = 10**6
T = [-1 for i in range(n)]
d = [INFTY for i in range(n)]
p = [0 for i in range(n)]
d[0], p[0] = 0, -1
for j in range(n):
    mincost = 10**6
    for i in range(n):
        if T[i] != 1 and d[i] < mincost:
            mincost = d[i]
            u = i
    T[u] = 1
    for v in range(n):
        if T[v] != 1 and A[u][v] != -1:
            if A[u][v] < d[v]:
                d[v] = A[u][v]
                p[v] = u
                T[v] = 0
print(sum(d))

Python: n = int(input())
edgeArray = [list(map(int, input().split())) for i in range(n)]
edgeList = []
rootList = [-1 for i in range(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]
        
for i in range(n):
    for j in range(i):
        if edgeArray[i][j] != -1:
            edgeList.append([edgeArray[i][j], i, j])
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: import sys
from collections import deque

sys.setrecursionlimit(1000000)
n = int(input())
graph = [[] for _ in range(n)]

global visited 
visited = [0 for _ in range(n)]
global Q, S, T

S = [0] #訪れた順
T = []
visited[0] = 1 #開始位置はすでに訪れたことにする

def input_graph(n):
  for i in range(n):
    vs = list(map(int, input().split()))
    graph[i] = vs
    """for j in range(n):
      if vs[j] != -1:
        tree[i].append([j, vs[j]])"""

def prim():
  global S
  cost = 0
  while len(S) < n:
    max_e = 3000
    ad_v = 0
    ad_list = []
    for s in S:
      for j in range(n):
        if graph[s][j] != -1 and j not in S:
          ad_list.append(graph[s][j])
          #print("s: ",s, " j: ",j, graph[s][j])
          if max_e > graph[s][j]:
            max_e = graph[s][j]
            ad_v = j
    S.append(ad_v)
    cost += max_e
  print(cost)
  

if __name__ == "__main__":
  input_graph(n)
  prim()

Python: import heapq
n = int(input())
ans = 0
cost = []
for i in range(n):
    L = list(map(int,input().split()))
    cost.append(L)
used = [False]*n
used[0] = True #島0から探索を始める。
edge = []
for i in range(n):
    T = []
    edge.append(T)
for i in range(n):
    for j in range(n):
        if cost[i][j] != -1:
            edge[i].append([cost[i][j],j])
P = edge[0]
P.sort()
while len(P) != 0:
    cur = heapq.heappop(P)
    d = cur[0]
    next = cur[1]
    if used[next] == True:
        continue
    used[next] = True
    ans += d
    for e in edge[next]:
        heapq.heappush(P,[e[0],e[1]])
print(ans)