Go: package main

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

// Node 頂点
type Node struct {
	gid  int   // グループID
	edge []int // 隣接辺
}

// NoID グループIDなし
const NoID = -1

// NewNode 頂点の生成
func NewNode() *Node {
	return &Node{gid: NoID, edge: []int{}}
}

func parseNode(nodes []*Node, gid int, queue []int) {
	if len(queue) == 0 {
		return
	}
	var nextQ []int
	for _, id := range queue {
		node := nodes[id]
		if node.gid == NoID {
			node.gid = gid
			for _, edge := range node.edge {
				nextQ = append(nextQ, edge)
			}
		}
	}
	parseNode(nodes, gid, nextQ)
	return
}
func digNode(nodes []*Node, id, gid int) {
	node := nodes[id]
	if node.gid != NoID {
		// 探索済み
		return
	}
	node.gid = gid
	for _, edge := range node.edge {
		digNode(nodes, edge, gid)
	}
	return
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n, m := eGetInt2(scanner)

	nodes := make([]*Node, n)
	for i := 0; i < n; i++ {
		nodes[i] = NewNode()
	}

	for i := 0; i < m; i++ {
		a, b := eGetInt2(scanner)
		nodes[a].edge = append(nodes[a].edge, b)
		nodes[b].edge = append(nodes[b].edge, a)
	}

	for i := 0; i < n; i++ {
		// 幅優先探索
		// gid := i
		// queue := []int{i}
		// parseNode(nodes, gid, queue)

		// 深さ優先探索
		digNode(nodes, i, i)
	}

	q := eGetInt(scanner)
	for i := 0; i < q; i++ {
		a, b := eGetInt2(scanner)
		if nodes[a].gid == nodes[b].gid {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}
func eGetInt2(scanner *bufio.Scanner) (int, int) {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0], t[1]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

Python: n, m = map(int, input().split())

adj = [[] for i in range(n)]

for i in range(m):
    s, t = map(int, input().split())
    adj[s].append(t)
    adj[t].append(s)

isVisited = [False] * n

CC = [None] * n

import sys
sys.setrecursionlimit(1000000)

def dfs(u, group):
    isVisited[u] = True
    CC[u] = group
    for v in adj[u]:
        if not isVisited[v]:
            dfs(v, group)

def makeCC(group):
    for i in range(n):
        if not isVisited[i]:
            dfs(i, group)
            group += 1

def isConnected(v1, v2):
    if CC[v1] == CC[v2]:
        print('yes')
    else:
        print('no')


makeCC(0)


q = int(input())

for i in range(q):
    s, t = map(int, input().split())
    isConnected(s, t)

Python: 
def BFS(s = 0, group_num = 0):
    Q.pop(0)
    color[s] = 2
    for j in range(len(A[s])):
        if color[A[s][j]] == 0:
            Q.append(A[s][j])
            color[A[s][j]] = 1
            affil[A[s][j]] = group_num
    if len(Q) != 0:
        BFS(Q[0], group_num)

n = 10
m = 9
friends = [[0, 1], [0, 2], [3, 4], [5, 7], [5, 6], [6, 7], [6, 8], [7, 8], [8, 9]]

A = [0] * n
for i in range(n):
    A[i] = list((-1, -1))
for i in range(m):
    entry = friends[i]
    s = entry[0]
    t = entry[1]
    A[s].append(t)
    A[t].append(s)

color = [0] * n
affil = [0] * n
group_num = -1
for i in range(n):
    if color[i] == 0:
        Q = [i]
        group_num = group_num + 1
        affil[i] = group_num
        BFS(i, group_num)

q = 3
quest = [[0, 1], [5, 9], [1, 3]]
for i in range(q):
    entry = quest[i]
    if affil[entry[0]] == affil[entry[1]]:
        print("yes")
    else:
        print("no")

Python: from collections import deque

n, m = map(int, input().split())

G = [[] for i in range(n)]


def bfs(s, e):
    check, dist = [0 for i in range(n)], [-1 for i in range(n)]
    q = deque()

    check[s], dist[s] = 1, 0
    q.append(s)

    while len(q) != 0:
        u = q.popleft()
        for v in range(len(G[u])):
            if check[G[u][v]] == 0:
                check[G[u][v]], dist[G[u][v]] = 1, dist[u] + 1
                q.append(G[u][v])

        check[u] = 2

    return dist[e]


def main():
    for i in range(m):
        a, b = map(int, input().split())
        G[a].append(b)
        G[b].append(a)

    q = int(input())

    for i in range(q):
        s, t = map(int, input().split())
        k = bfs(s, t)
        if k == -1:
            print("no")
        else:
            print("yes")


if __name__ == '__main__':
    main()

Python: from collections import deque


def bfs(root):
    global time
    Q = deque()
    distance[root] = 0
    Q.append(root)
    i = root
    while len(Q) > 0:
        i = Q.popleft()
        for v in range(n):
            if v in adjDict[i] and color[v] == 'white':
                Q.append(v)
                color[v] = 'gray'
                distance[v] = distance[i] + 1
        color[i] = 'black'
        label[i] = time


firstline = list(map(int, input().split()))

n = firstline[0]
adjDict = {i: [] for i in range(n)}
color = ['white'] * n
distance = [-1] * n
label = [-1] * n

m = firstline[1]
for _ in range(m):
    adj = list(map(int, input().split()))
    adjDict[adj[0]].append(adj[1])

time = 0
for i in range(n):
    if color[i] == 'white':
        bfs(i)
        time += 1

q = int(input())
for _ in range(q):
    question = list(map(int, input().split()))
    if label[question[0]] == label[question[1]]:
        print('yes')
    else:
        print('no')

Python: import sys
sys.setrecursionlimit(200000)
input_lines = [[int(i) for i in line.split()] for line in sys.stdin.read().splitlines()]
[user_num, rel_num] = input_lines[0]
rel_list = input_lines[1:rel_num+1]
ques_num = input_lines[rel_num+1][0]
ques_list = input_lines[rel_num+2:]
color_list = [-1] * user_num
adja_list = [set() for i in range(user_num)]

def dfs(id, color):
    if color_list[id] == -1:
        color_list[id] = color
        for a_id in adja_list[id]:
            dfs(a_id, color)



for rel in rel_list:
    adja_list[rel[0]].add(rel[1])
    adja_list[rel[1]].add(rel[0])

color = 0
for id in range(user_num):
    dfs(id, color)
    color += 1

for ques in ques_list:
    if color_list[ques[0]] == color_list[ques[1]]:
        print('yes')
    else:
        print('no')

Python: import sys
sys.setrecursionlimit(10000)

def connected(G,s,t):
    checked = [False]*len(G)
    def main(G,s,t):
        if t in G[s]: return True
        checked[s] = True
        for f in G[s]:
            if checked[f]: continue
            if main(G,f,t): return True
        return False
    return main(G,s,t)
        

if __name__=='__main__':
    n,m = list(map(int,input().split()))
    G = [[] for _ in range(n)]
    for _ in range(m):
        s,t = list(map(int,input().split()))
        G[s].append(t)
        G[t].append(s)
    q = int(input())
    for _ in range(q):
        s,t = list(map(int,input().split()))
        print('yes' if connected(G,s,t) else 'no')