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: 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")