Go: package main

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

const MAX = 100000

type Queue struct {
	head      int
	tail      int
	container [MAX]int
}

func (q *Queue) push(n int) {
	q.container[q.tail] = n
	q.tail = (q.tail + 1) % MAX
}

func (q *Queue) pop() int {
	res := q.container[q.head]
	q.head = (q.head + 1) % MAX
	return res
}

func (q *Queue) isEmpty() bool {
	return q.head == q.tail
}

var sc = bufio.NewScanner(os.Stdin)
var route [][]int
var SEEN [MAX]bool
var GROUP [MAX]int

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

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

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

func bfs(start, group int) {
	que := Queue{}
	que.push(start)

	for !que.isEmpty() {
		id := que.pop()

		if SEEN[id] {
			continue
		}
		SEEN[id] = true
		GROUP[id] = group

		for _, next := range route[id] {
			que.push(next)
		}
	}
}

func main() {
	n, m := scanInt(), scanInt()
	route = make([][]int, n)
	for i := 0; i < m; i++ {
		s, t := scanInt(), scanInt()
		route[s] = append(route[s], t)
		route[t] = append(route[t], s)
	}

	for i := 0; i < n; i++ {
		if !SEEN[i] {
			bfs(i, i+1)
		}
	}

	w := bufio.NewWriter(os.Stdout)
	q := scanInt()
	for i := 0; i < q; i++ {
		s, t := scanInt(), scanInt()
		if GROUP[s] == GROUP[t] {
			fmt.Fprintln(w, "yes")
		} else {
			fmt.Fprintln(w, "no")
		}
	}
	w.Flush()
}

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(10000000000000)

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: from sys import stdin
n, m = map(int, stdin.readline().split())
G = [-1] * n
def root(x):
    if G[x] < 0: return x
    G[x] = root(G[x])
    return G[x]
def uniteSet(x, y):
    x = root(x)
    y = root(y)
    if x == y : return
    if G[x] > G[y] : x, y = y, x
    G[y] = x
def findSet(x, y): return root(x) == root(y)
for i in range(0, m):
    s, t = map(int, stdin.readline().split())
    uniteSet(s, t)
q = int(stdin.readline())
for i in range(0, q):
    s, t = map(int, stdin.readline().split())
    print("yes" if findSet(s, t) else "no")

Python: #coding: utf-8

n, m = map(int,input().split())
List = [[] for i in range(n)]
colorOriginal = ["white" for i in range(n)]

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



class DoublyLinkedList():
    def __init__(self, key, l=None, r=None):
        self.l = l
        self.r = r
        self.key = key

def Insert(key,sentinel):
    obj = DoublyLinkedList(key)
    left = sentinel.l
    left.r = obj
    obj.l = left
    obj.r = sentinel
    sentinel.l = obj

def deleteFirst(sentinel):
    right = sentinel.r
    sentinel.r = right.r
    right.r.l = sentinel


def search(a, target):
    sentinel = DoublyLinkedList(None)
    sentinel.l = sentinel
    sentinel.r = sentinel
    
    color = colorOriginal[:]
    Insert(a, sentinel)
    color[a] = "black"
    while sentinel.r.key != None:
        top = sentinel.r.key
        if top == target:
            print("yes")
            break
        for i in List[top]:
            if color[i] == "white":
                Insert(i, sentinel)
                color[i] = "gray"
        color[top] = "black"
        deleteFirst(sentinel)
    else:
        print("no")

ques = int(input())
for i in range(ques):
    a, target = map(int,input().split())
    search(a, target)

Python: from collections import deque

def bfs(graph, start, goal):
    visited = {start: None}
    unvisited = deque()
    unvisited.append(start)
    while unvisited:
        now = unvisited.popleft()
        if now == goal or goal in graph[now]:
            graph[start].add(goal)
            graph[goal].add(start)
            return "yes"
        for next in graph[now]:
            if not (next in visited):
                unvisited.append(next)
                visited[next] = now
    return "no"

n, m = map(int, input().split())
g = [set() for i in range(n)]

for i in range(m):
    a, b = map(int, input().split())
    g[a].add(b)
    g[b].add(a)

q = int(input())

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

Python: import sys
sys.setrecursionlimit(1000000)
n, m = map(int, input().split())
graph = [[] for _ in range(n)]

global visited 
visited = [0 for _ in range(n)]

def input_graph(m):
  for _ in range(m):
    u, v = map(int, input().split())
    graph[u].append(v)
    graph[v].append(u)

def dfs(node_id):
  
  for ad_node in graph[node_id]:
    if visited[ad_node] == 1:
      continue
    visited[ad_node] = 1
    dfs(ad_node)

if __name__ == "__main__":
  input_graph(m)
  q_num = int(input())
  for _ in range(q_num):
    visited = [0 for _ in range(n)]
    s, t = map(int, input().split())
    dfs(s)
    if visited[t]:
      print("yes")
    else:
      print("no")

Python: #!/usr/bin/python3
n, m = map(int, input().split())

e = [None] * n

for i in range(m):
    s, t = map(int, input().split())
    if e[s] == None and e[t] == None:
        a = {s, t}
        e[s] = e[t] = a
    elif e[s] == None:
        e[t].add(s)
        e[s] = e[t]
    elif e[t] == None:
        e[s].add(t)
        e[t] = e[s]
    else:
        a = e[s] | e[t]
        for j in a:
            e[j] = a

q = int(input())
for i in range(q):
    s, t = map(int, input().split())
    if t in e[s]:
        print('yes')
    else:
        print('no')

Python: from collections import deque
n,m = [int(i) for i in input().split()]
F = [{} for i in range(n)]
for _ in range(m):
    i,j = [int(i) for i in input().split()]
    F[i][j] = 1
    F[j][i] = 1
q = int(input())
for i in range(q):
    DP = [0]*n
    d = deque()
    s,t = [int(i) for i in input().split()]
    d.append(s)
    flag = False
    while(len(d)>0):
        tmp = d.pop()
        DP[tmp] = 1
        if tmp == t:
            flag = True
            break
        else:
            for i in F[tmp]:
                if not DP[i]:
                    d.append(i)
    if flag:
        print("yes")
    else:
        print("no")

Python: import collections
import sys
sys.setrecursionlimit(100000)

n, m = [int(ele) for ele in input().split()]
graph = [[i] for i in range(n)]
grps = [-1] * n
s = [-1] * (m+1)
t = [-1] * (m+1)

for _ in range(m):
    k, l = [int(ele) for ele in input().split()]
    graph[k].append(l)
    graph[l].append(k)

q = int(input())

s_q = [-1] * (q)
s_t = [-1] * (q)

for i in range(q):
    s_q[i], s_t[i] = [int(ele) for ele in input().split()]


yet = [ele for ele in range(n)]
stack = collections.deque()


def main():
    global graph, grps
    grouping()

    for src, dst in zip(s_q, s_t):
        if grps[src] == grps[dst]:
            print("yes")
        else:
            print("no")


def grouping():
    global yet, stack, grps, tmp
    tmp = 97
    while yet:
        stack.clear()
        stack.appendleft(yet[0])  # 常にmin(yet) = yet[0]
        dfs(stack)
        tmp += 1


def dfs(stack):
    global yet, graph, grps, tmp
    if not stack:
        return

    n = stack[0]
    grps[n] = chr(tmp)
    yet.remove(n)

    for ele in graph[n][1:]:
        if ele in yet:  # 未訪問なら
            stack.appendleft(ele)
            dfs(stack)
    else:
        stack.popleft()


if __name__ == "__main__":
    main()