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: import sys
def s():
 e=sys.stdin.readline
 n,m=map(int,e().split())
 P=[[]for _ in[0]*n]
 C=[0]*n
 k=0
 for _ in[0]*m:
  s,t=map(int,e().split());P[s]+=[t];P[t]+=[s]
 for i in range(n):
  k+=1
  if C[i]<1:
   s=[i];C[i]=k
   while s:
    u=s.pop()
    for v in P[u]:
     if C[v]<1:C[v]=k;s+=[v]
 for _ in[0]*int(e()):
  a,b=map(int,e().split())
  print(['no','yes'][C[a]==C[b]])
if'__main__'==__name__:s()

Python: def main():
    class UnionFind:
        def __init__(self, n=0):
            self.d = [-1]*n

        def root(self, x):
            if self.d[x] < 0:
                return x
            self.d[x] = self.root(self.d[x])
            return self.d[x]

        def unite(self, x, y):
            x, y = self.root(x), self.root(y)
            if x == y:
                return False
            if x > y:
                x, y = y, x
            self.d[x] += self.d[y]
            self.d[y] = x
            return True

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

    raw = tuple(map(int, open(0).read().split()))
    n, m = raw[:2]
    uf = UnionFind(n)
    [uf.unite(a, b) for a, b in zip(*[iter(raw[2:2*m+2])]*2)]

    [print('yes' if uf.same(a, b) else 'no') for a, b in zip(*[iter(raw[2*m+3:])]*2)]

if __name__ == '__main__':
    main()

Python: n, m = map(int, input().split())

a = [[] for i in range(n)]

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

q = int(input())

from collections import deque
for j in range(q):
    queue = deque()
    memo = [0 for i in range(n)]
    data = list(map(int, input().split()))
    memo[data[0]] = 1
    queue.append(data[0])

    try:
        while len(queue):
            b = queue.popleft()
            if len(a[b]):
                for k in a[b]:
                    if k == data[1]:
                        print("yes")
                        raise Exception
                    if memo[k] == 0:
                        memo[k] = 1
                        queue.append(k)
        print("no")
    except Exception:
        pass

Python: # -*- coding: utf-8 -*-
"""
Created on Sat Jul 14 10:14:13 2018
ALDS1_11_D
@author: maezawa
"""
import sys
sys.setrecursionlimit(1000000)

n, m = list(map(int, input().split()))
v = [-1 for _ in range(n)]
stack = []
adj = [[] for _ in range(n)]
for i in range(m):
    s, t = list(map(int, input().split()))
    adj[s].append(t)
    adj[t].append(s)
#print(*adj, sep='\n')
def dfs(u, color):
    if v[u] > 0:
        return 0
    v[u] = color
    #print(u, current, stack)
    for k in adj[u]:
        if v[k] > 0:
            continue
        dfs(k, color)
    return 1

color = 1
for start in range(n):
    if dfs(start, color) == 1:
        color += 1
#for i in range(n):        
#    print('color:{} for node:{}'.format(i, v[i]))

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

Python: def bfs(graph, start, goal, connection):
    visited = {start: None}
    unvisited = [start]
    while unvisited:
        now = unvisited[0]
        if now == goal or (1000000*now + goal) in connection:
            connection[1000000*start + goal] = 1
            connection[1000000*goal + start] = 1
            return "yes"
        unvisited = unvisited[1:]
        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 = [[] for i in range(n)]
c = {}

for i in range(m):
    inp = list(map(int, input().split()))
    g[inp[0]].append(inp[1])
    g[inp[1]].append(inp[0])
    c[1000000*inp[0] + inp[1]] = 1
    c[1000000*inp[1] + inp[0]] = 1

q = int(input())

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

Python: def DFS(s):
    flag[s] = 1
    F[group] = F[group] + s
    for i in range(n):
        if G[s][i] == 1:
            if flag[i] == 0:
                DFS(i)
 

n, m = map(int, input().split())
G = [[0 for i in range(n)] for j in range(n)]
for i in range(m):
    s, t = map(int, input().split())
    G[s][t] = 1
    G[t][s] = 1

F = []
flag = [0 for i in range(n)]
group = 0
for i in range(n):
    if flag[i] == 0:
        F.append([])
        DFS(i)
        group += 1

q = int(input())
ans = ["no" for i in range(q)]
for i in range(q):
    s, t = map(int, input().split())
    for friends in F:
        if s in friends and t in friends:
            ans[i] = "yes"

for i in range(q):
    print(ans[i])