Go: package main

import (
	"bufio"
	"container/list"
	"os"
	"strconv"
	"fmt"
)

const (
	MAX = 100000
	NIL = -1
)

var (
	n     int
	G     [MAX][]int
	color [MAX]int
)

func DFS(r int, c int) {
	S := list.New()
	S.PushFront(r)
	color[r] = c
	for S.Len() != 0 {
		u := S.Remove(S.Front()).(int)
		for i := 0; i < len(G[u]); i++ {
			v := G[u][i]
			if color[v] == NIL {
				color[v] = c
				S.PushFront(v)
			}
		}
	}
}

func assignColor() {
	id := 1
	for i := 0; i < n; i++ {
		color[i] = NIL
	}
	for i := 0; i < n; i++ {
		if color[i] == NIL {
			id++
			DFS(i, id)
		}
	}
}

func main() {
	var s, t, m, q int
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	n, _ = strconv.Atoi(scanner.Text())
	scanner.Scan()
	m, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < m; i++ {
		scanner.Scan()
		s, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()
		t, _ = strconv.Atoi(scanner.Text())
		if i == 0 {
			G[s] = make([]int, 0)
			G[t] = make([]int, 0)
		}
		G[s] = append(G[s], t)
		G[t] = append(G[t], s)
	}

	assignColor()
	scanner.Scan()
	q, _ = strconv.Atoi(scanner.Text())
	for i := 0; i < q; i++ {
		scanner.Scan()
		s, _ = strconv.Atoi(scanner.Text())
		scanner.Scan()
		t, _ = strconv.Atoi(scanner.Text())
		if color[s] == color[t] {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

Python: import sys
sys.setrecursionlimit(10**6)


def dfs(v, cnt):
    group[v] = cnt
    for c in edge[v]:
        if group[c] == -1:
            dfs(c, cnt)

V, E = map(int, input().split())
edge = [[] for _ in range(V)]
for _ in range(E):
    s, t = map(int, input().split())
    edge[s].append(t)
    edge[t].append(s)
group = [-1] * V
c = 0
for i in range(V):
    if group[i] == -1:
        dfs(i, c)
        c += 1

Q = int(input())
for _ in range(Q):
    s, t = map(int, input().split())
    print('yes' if group[s] == group[t] else 'no')

Python: #coding:utf-8
import sys
sys.setrecursionlimit(100000)
n, r = map(int,input().split())
Q = []
M = [[] for j in range(n)]
for i in range(r):
    i,j = map(int,input().split())
    M[i].append(j)
    M[j].append(i)


def search(person, target):
    global yes
    if yes == 1:
        return
    data = M[person]
    for per in data:
        if per ==  target:
            yes = 1
            return
        if color[per] == "white":
            color[per] = "gray"
            search(per, target)
    color[person] = "black"

num = int(input())
for i in range(num):
    yes = 0
    color = ["white" for j in range(n)]
    person, target = map(int,input().split())
    search(person, target)
    if yes == 0:
        print("no")
    else:
        print("yes")

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)
    return group_num

entry = map(int, raw_input())
n = entry[0]
m = entry[1]

A = range(n)
for i in A:
    A[i] = list()
for i in range(m):
    entry = map(int, raw_input())
    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]
        affil[i] = group_num + 1
        group_num = BFS(i, group_num + 1)

q = int(raw_input())
for i in range(q):
    entry = map(int, raw_input())
    if affil[entry[0]] == affil[entry[1]]:
        print("yes")
    else:
        print("no")

Python: import sys
# sys.stdin = open('input.txt')

def dfs(r, c):
    S = []
    S.append(r)
    color[r] = c
    while len(S) > 0:
        u = S.pop()
        for v in G[u]:
            if color[v] is None:
                color[v] = c
                S.append(v)

def assignColors():
    colorId = 0
    for i in range(n):
        if color[i] is None:
            dfs(i, colorId)
            colorId += 1

n, m  = map(int, input().split())
G = [[] for _ in range(n)]
color = [None] * n

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

assignColors()

q = int(input())
for i in range(q):
    s, t = map(int, input().split())
    if color[s] is not None and color[s] == color[t]:
        print('yes')
    else:
        print('no')

Python: from collections import deque

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

while m:
    s, t = map(int, input().split())
    g[s].add(t)
    g[t].add(s)
    m -= 1


def find(s, t):
    global g
    queue = deque()
    queue.append((0, s))
    queue.append((1, t))
    visited = ([0] * n, [0] * n)
    visited[0][s] = 1
    visited[1][t] = 1

    def remember(visited, new):
        for i, v in enumerate(visited):
            if v:
                g[new].add(i)
                g[i].add(new)
        visited[new] = 1

    while queue:
        st, i = queue.popleft()
        for f in g[i]:
            if visited[not st][f]:
                return True
            if not visited[st][f]:
                remember(visited[st], f)
                queue.append((st, f))
    return False


q = int(input())
while q:
    s, t = map(int, input().split())
    print('yes' if find(s, t) else 'no')
    q -= 1

Python: n, m = map(int, input().split())
rootList = [-1 for i in range(n)]
 
def getRoot(x):
    if rootList[x] < 0:
        rootList[x] = x
        return x
    return getRoot(rootList[x])
 
 
def setSameRoot(x, y):
    x = getRoot(x)
    y = getRoot(y)
    if x != y:
        rootList[x], rootList[y] = min(x, y), min(x, y)
 
for i in range(m):
    s, t = map(int, input().split())
    setSameRoot(s, t)
q = int(input())
for i in range(q):
    s, t = map(int, input().split())
    print("yes" if getRoot(s) == getRoot(t) != -1 else "no")

Python: class UnionFind:
    def __init__(self,n):
        self.n = n
        self.p = [i for i in range(n)]
        self.rank = [0]*n

    def same(self,x,y):
        return self.root(x)==self.root(y)

    def root(self,x):
        if x!=self.p[x]:self.p[x] = self.root(self.p[x])
        return self.p[x]

    def unite(self,x,y):
        x = self.root(x)
        y = self.root(y)
        if self.rank[y]<self.rank[x]:
            self.p[y] = x
        else:
            self.p[x] = y
            if self.rank[y]==self.rank[x]:
                self.rank[y]+=1

def main():
    n,m = map(int,input().split())
    UF = UnionFind(n)
    for _ in range(m):
        a,b = map(int,input().split())
        UF.unite(a,b)
    q = int(input())
    for _ in range(q):
        a,b = map(int,input().split())
        if UF.same(a,b):print ('yes')
        else           :print ('no')


if __name__ == '__main__':
    main()

Python: from collections import deque


user_num,rer_num=map(int,input().split())
graph=[[] for loop in range(user_num)]

for loop in range(rer_num):
    user1,user2=map(int,input().split())
    graph[user1].append(user2)
    graph[user2].append(user1)

#group[user1]はuser1が属するグループ.同じグループに属するuser同士は互いに到達可能
group=[-1]*user_num

que=deque([])
que.append(0)
tmp_group=0
for user in range(user_num):
    if(group[user]==-1):
        que.append(user)
        group[user]=tmp_group
        while(1):
            user1=que.popleft()
            for user2 in graph[user1]:
                if(group[user2]==-1):
                    que.append(user2)
                    group[user2]=tmp_group
            if(len(que)==0):
                tmp_group+=1
                break

for loop in range(int(input())):
    user1,user2=map(int,input().split())
    if(group[user1]==group[user2]):
        print("yes")
    else:
        print("no")