Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func newGraph(nNodes int) *Graph {
	g := Graph{}
	g.nodes = make([]*GraphNode, nNodes)
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode] = &GraphNode{}
		g.nodes[iNode].key = GraphNodeKey(iNode)
	}
	return &g
}

var infty = 1000000000

type GraphNodeKey int

// GraphNode is a node for undirected graph
type GraphNode struct {
	key       GraphNodeKey
	adjacents []*GraphNode
	visited   bool
	d, f      int
	parent    *GraphNode
	cc        int
}

func (g *Graph) setAdjacent(l, r GraphNodeKey) {
	g.nodes[l].adjacents = append(g.nodes[l].adjacents, g.nodes[r])
}

// Graph is a undirected graph
type Graph struct {
	nodes []*GraphNode
}

func (g *Graph) initialize() {
	for iNode := 0; iNode < len(g.nodes); iNode++ {
		g.nodes[iNode].visited = false
		g.nodes[iNode].d = infty
		g.nodes[iNode].f = infty
		g.nodes[iNode].parent = nil
		g.nodes[iNode].cc = -1 // 22.3-12
	}
}

type QueueEntry struct {
	node *GraphNode
	next *QueueEntry
}

type Queue struct {
	head, tail *QueueEntry
}

func (q *Queue) enqueue(node *GraphNode) {
	entry := QueueEntry{}
	entry.node = node

	if q.tail == nil {
		q.head = &entry
		q.tail = &entry
		return
	}

	q.tail.next = &entry
	q.tail = q.tail.next
}

func (q *Queue) dequeue() *QueueEntry {
	if q.head == nil {
		return nil
	}
	poped := q.head
	q.head = q.head.next
	if q.head == nil {
		q.tail = nil
	}
	return poped
}

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

var time = 0

func fillDistancesByDepthFirstSearch(g *Graph) {
	g.initialize()
	time = 0
	cc := 0

	for _, u := range g.nodes {
		if !u.visited {
			dfsVisit(g, u, cc)
			cc++
		}
	}
}

func dfsVisit(g *Graph, u *GraphNode, cc int) {
	time++
	u.d = time
	u.cc = cc

	u.visited = true
	for _, v := range u.adjacents {
		if !v.visited {
			v.parent = u
			dfsVisit(g, v, cc)
		}
	}
	time++
	u.f = time
}

func main() {
	scanner.Split(bufio.ScanWords)

	nUsers := nextInt()
	nEdges := nextInt()
	graph := newGraph(nUsers)
	for iEdge := 0; iEdge < nEdges; iEdge++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())
		graph.setAdjacent(l, r)
		graph.setAdjacent(r, l)
	}

	fillDistancesByDepthFirstSearch(graph)

	nQueries := nextInt()
	for iQuery := 0; iQuery < nQueries; iQuery++ {
		l := GraphNodeKey(nextInt())
		r := GraphNodeKey(nextInt())

		// fmt.Println(graph.nodes[l].d, graph.nodes[r].d, graph.nodes[r].f, graph.nodes[l].f)
		if graph.nodes[l].cc == graph.nodes[r].cc {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

Python: # -*- coding: utf-8 -*-

def assignColor(G):
    n = len(G)
    C = [-1 for i in range(n)]
    for i in range(n):
        if C[i] == -1:
            C = BFS(G, i, C)
    return C
        
def BFS(G, start, C):
    n = len(G)
    flag = [0] * n
    Q = []

    Q.append(start)
    C[start] = start
    flag[start] = 1

    while len(Q) != 0:
        u = Q.pop(0)
        v = [i for i in G[u] if flag[i] == 0] # v := ??£??\???????????????????????¢?´¢??????????????????
        
        for i in v:
            Q.append(i)
            C[i] = C[start]
            flag[i] = 1
    
    return C

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

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

    C = assignColor(G)
        
    q = int(input())
    
    for i in range(q):
        s, t = list(map(int, input().split()))
        if C[s] == C[t]:
            print("yes")
        else:
            print("no")
            
if __name__ == "__main__":
    main()

Python: import sys
readline = sys.stdin.readline
def MAIN():
    n, m = map(int, input().split())
    li = [i for i in range(n)]
    def f(a):
        if li[a] == a:
            return a
        li[a] = f(li[a])
        return li[a]
    def f2(a, b):
        if li[a] == a:
            li[a] = b
            return
        f2(li[a], b)
        li[a] = b
    for _ in range(m):
        x, y = map(int, readline().split())
        if f(x) > f(y):
            f2(x, li[y])
        elif f(x) < f(y):
            f2(y, li[x])
    for _ in range(int(input())):
        x, y = map(int, readline().split())
        print("yes" if f(x) == f(y) else "no")
MAIN()

Python: import sys
from collections import defaultdict

def main():
    lines = sys.stdin.readlines()
    n, m = map(int, lines[0].split())
    relation_lines = lines[1:1+m]

    relations = defaultdict(list)

    for idx, relation_line in enumerate(relation_lines):
        s, t = relation_line.split()
        relations[s].append(t)
        relations[t].append(s)

    group = {}
    for key in relations.keys():
        group[key] = -1
    group_num = 0

    # assign a group number for ids
    for key, val in relations.items():
        if group[key] != -1:
            continue

        group[key] = group_num
        group_num += 1

        group_no = group[key]
        friends = [key]

        while len(friends) != 0:
            n_fs = relations[friends.pop()]
            for n_f in n_fs:
                if group[n_f] == -1:
                    group[n_f] = group_no
                    friends.append(n_f)

    q = int(lines[1+m])
    question_lines = lines[1+m+1:]
    answers = [None] * q
    for i, question in enumerate(question_lines):
        s, t = question.split()

        if s not in group or t not in group:
            answers[i] = 'no'
            continue
        elif group[s] == group[t]:
            answers[i] = 'yes'
        else:
            answers[i] = 'no'

    # answer
    [print(ans) for ans in answers]
    return

main()

Python: n, m = map(int, raw_input().split())
G = [[0 for i in range(n)] for j in range(n)]

for i in range(m):
    s, t = map(int, raw_input().split())
    G[s][t] = 1
    G[t][s] = 1

for i in range(n):
    for j in range(n):
        for k in range(n):
            if G[j][k] == 1:
                for l in range(k+1, n):
                    if G[k][l] == 1:
                        G[j][l] = 1

q = int(raw_input())
ans = ["no" for i in range(q)]
for i in range(q):
    s, t = map(int, raw_input().split())
    if G[s][t] == 1:
        ans[i] = "yes"
for i in range(q):
    print(ans[i])

Python: def dfs(r, c):
    global c, color, G
    S = [r]
    color[r] = c
    while (0 < len(S)):
        u = S.pop()
        for u in G[u]:
            v = color[ch]
            if (v == False):
                color[u] = c
                S.append(u)
 
def assignColor():
    global c, color, G, n
    c = 1
    for i in range(n):
        if (color[i] == False):
            dfs(i, c)
            c += 1
 
n, m = list(map(int, input().split()))
 
G = [False for i in range(n)]
for i in range(m):
    s, t = list(map(int, input().split()))
    G[s].append(t)
    G[t].append(s)
 
color = [False for i in range(n)]
 
assignColor()
 
q = int(input())

for i in range(q):
    s, t = list(map(int, input().split()))
    if (color[s] == color[t]):
        print("yes")
    else:
        print("no")

Python: n, m = map(int, input().split())
rootList = [-1] * n

def getRoot(x):
    if rootList[x] < 0:
        return x
    rootList[x] = getRoot(rootList[x])
    return rootList[x]

def setSameRoot(x, y):
    x = getRoot(x)
    y = getRoot(y)
    if x != y:
        G[x], G[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")