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: #!/usr/bin/python3
n, m = map(int, input().split())
ALL = [0] * n
Graph = []
for i in range(m):
    s, t = map(int, input().split())
    if ALL[s] == 0 and ALL[t] == 0:
        Graph.append(set([s, t]))
    elif ALL[s] == 0:
        for g in Graph:
            if t in g:
                g.add(s)
                break
    elif ALL[t] == 0:
        for g in Graph:
            if s in g:
                g.add(t)
                break
    else:
        sg = None
        tg = None
        for g in Graph:
            if s in g:
                sg = g
            if t in g:
                tg = g

        if sg is not tg:
            sg.update(tg)
            Graph.remove(tg)

    ALL[s] = 1
    ALL[t] = 1
q = int(input())
for i in range(q):
    s, t = map(int, input().split())
    for g in Graph:
        if s in g and t in g:
            print('yes')
            break
    else:
        print('no')

Python: def tan(G,st,fi):
    for i in range(len(G)):
        if G[st][i] == 1:
            if i == fi:
                return 1
            tan(G,i,fi)
    
n,m = list(map(int, input().split()))
G = [[0 for i in range(n)] for j in range(n)]

for i in range(m):
    S = list(map(int, input().split()))
    G[S[0]][S[1]] = 1

q = int(input())
ans = []
for i in range(q):
    Q = list(map(int, input().split()))
    st = Q[0]
    fi = Q[1]
    if(tan(G,Q[0],Q[1])):
        ans.append("yes")
    else:
        ans.append("no")
        
for i in range(q):
    print(ans[i])

Python: def bfs(adj, s):
    n = len(adj)
    d = [-1 for _ in range(n)]
    c = [0 for _ in range(n)]

    d[s] = 0
    c[s] = 1

    queue = [s]

    while len(queue) > 0:
        u = queue.pop(0)
        for v in adj[u]:
            if c[v] == 0:
                c[v] = 1
                d[v] = d[u] + 1
                queue.append(v)

    return d


s = [int(x) for x in input().split()]
n = s[0]
m = s[1]
adj = [[] for _ in range(n)]
for _ in range(m):
    s = [int(x) for x in input().split()]
    adj[s[0]].append(s[1])
    adj[s[1]].append(s[0])

q = int(input())
for _ in range(q):
    s = [int(x) for x in input().split()]
    u = s[0]
    v = s[1]
    d = bfs(adj, u)
    if d[v] > 0:
        print("yes")
    else:
        print("no")

Python: from collections import deque

def bfs(graph, start):
    visited = {start: None}
    unvisited = deque()
    unvisited.append(start)
    while unvisited:
        now = unvisited.popleft()
        for next in graph[now]:
            if not (next in visited):
                unvisited.append(next)
                visited[next] = now
    return  visited                                

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

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())
    for j in range(len(group)):
        if s in group[j] and t in group[j]:
            print('yes')
            break
        elif s in group[j]:
            print('no')
            break
    
    else:
        group_tmp = set(bfs(g, s).keys())
        if t in group_tmp:
            print('yes')
        else:
            print('no')
        group.append(group_tmp)

Python: 
NIL = -1

def assignColor():
    id = 1
    for i in range(n):
        color[i] = NIL
    for u in range(n):
        if color[u] == NIL:
            dfs(u, id)
            id += 1

def dfs(r, c):
    S = []
    S.append(r)
    color[r] = c
    while S:
        u = S.pop()
        for v in (G[u]):
            if color[v] == NIL:
                color[v] = c
                S.append(v)


nums=list(map(int,input().split()))
n = nums[0]
m = nums[1]
G = []
color = [NIL] * n

for i in range(n):
    G.append(set())
    
for i in range(m):
    nodes=list(map(int,input().split()))
    G[nodes[0]].add(nodes[1])
    G[nodes[1]].add(nodes[0])

assignColor()

q = int(input())
for i in range(q):
    questions=list(map(int,input().split()))
    if color[questions[0]] == color[questions[1]]:
        print("yes")
    else:
        print("no")

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)

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