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: class UnionFind:
    def __init__(self, n: int):
        self.nodes = n
        self.parents = [-1] * n
        self.rank = [0] * n

    # retrun the root of element x
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    # unite the group include element x and group include element y
    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.rank[x] < self.rank[y]:
            self.parents[y] += self.parents[x]
            self.parents[x] = y
        else:
            self.parents[x] += self.parents[y]
            self.parents[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # get size of the gourp which element x belongs
    def get_size(self, x):
        return -self.parents[self.find(x)]

    # check if element x and element y is same group
    def same(self, x, y):
        return self.find(x) == self.find(y)


n, m = [int(i) for i in input().split()]
union = UnionFind(n)
for _ in range(m):
    s, t = [int(i) for i in input().split()]
    union.unite(s, t)

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

Python: #coding:utf-8
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):
    data = M[person]
    for per in data:
        if per ==  target:
            global yes
            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: #!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def assign_color():
    _id = 1
    for m in range(vertices_num):
        if vertices_status_list[m] == -1:
            graph_dfs(m, _id)
            _id += 1
    return None


def graph_dfs(vertex, color):
    vertices_stack = list()
    vertices_stack.append(vertex)
    vertices_status_list[vertex] = color
    while vertices_stack:
        current_vertex = vertices_stack[-1]
        vertices_stack.pop()
        for v in adj_list[current_vertex]:
            if vertices_status_list[v] == -1:
                vertices_status_list[v] = color
                vertices_stack.append(v)
    return None


if __name__ == '__main__':
    _input = sys.stdin.readlines()
    vertices_num, relation_num = map(int, _input[0].split())

    relation_info = _input[1:relation_num + 1]

    question_num = int(_input[relation_num + 1])
    question_list = _input[relation_num + 2:]

    adj_list = [[] for _ in range(vertices_num)]
    vertices_status_list = [-1] * vertices_num

    for relation in relation_info:
        key, value = map(int, relation.split())
        adj_list[key].append(value)
        adj_list[value].append(key)

    assign_color()

    # print(adj_list)
    for question in question_list:
        start, target = map(int, question.split())
        if vertices_status_list[start] == vertices_status_list[target]:
            print("yes")
        else:
            print("no")

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

import sys

sys.setrecursionlimit(10 ** 9)
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
INF=float('inf')

N,M=MAP()
nodes=[[] for i in range(N)]
for i in range(M):
    s,t=MAP()
    nodes[s].append(t)
    nodes[t].append(s)

group=[-1]*N
def rec(u, root):
    if group[u]!=-1:
        return
    group[u]=root
    for v in nodes[u]:
        rec(v, root)

for i in range(N):
    rec(i, i)

Q=INT()
for _ in range(Q):
    s,t=MAP()
    if group[s]==group[t]:
        print('yes')
    else:
        print('no')