Go: // AOJ ALDS1_11_D: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_11_D

package main

import (
	"bufio"
	"container/list"
	"fmt"
	"os"
	"strconv"
)

var nocolor = -1

type graph struct {
	graph  [][]int
	colors []int
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

func newGraph(nodeNum int) *graph {
	colors := make([]int, nodeNum)
	g := make([][]int, nodeNum)
	for i := 0; i < nodeNum; i++ {
		g[i] = []int{}
		colors[i] = nocolor
	}

	return &graph{g, colors}
}

func constructGraph(sc *bufio.Scanner) *graph {
	usersNum := nextInt(sc)
	linkNum := nextInt(sc)

	g := newGraph(usersNum)
	for i := 0; i < linkNum; i++ {
		u := nextInt(sc) // node
		l := nextInt(sc) // link node
		// edge each other
		g.graph[u] = append(g.graph[u], l)
		g.graph[l] = append(g.graph[l], u)
	}
	return g
}

func (g *graph) dfs(r, color int) {
	g.colors[r] = color

	stack := list.New()
	stack.PushFront(r)

	for stack.Len() > 0 {
		v := stack.Remove(stack.Front()).(int)
		for _, u := range g.graph[v] {
			if g.colors[u] == nocolor {
				g.colors[u] = color
				stack.PushFront(u)
			}
		}
	}
}

func (g *graph) assignColor() {
	color := 1
	for u := 0; u < len(g.graph); u++ {
		if g.colors[u] == nocolor {
			g.dfs(u, color)
			color++
		}
	}
}

func (g *graph) isLink(s, t int) bool {
	return g.colors[s] == g.colors[t]
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	// construct graph and friendly colors
	g := constructGraph(sc)
	g.assignColor()

	// judge link
	q := nextInt(sc)
	for i := 0; i < q; i++ {
		s := nextInt(sc)
		t := nextInt(sc)

		if g.isLink(s, t) {
			fmt.Println("yes")
		} else {
			fmt.Println("no")
		}
	}
}

Python: # -*- coding: utf_8 -*-

level = False
def debug(v):
    if level:
        print(v)

NOT_FOUND = 0
ENQUEUED = 1
FOUND = 2

def bfs(graph, start, target):
    debug(graph)
    if start == target:
        return True
    
    queue = []
    status = [NOT_FOUND] * len(graph)
    queue.append(start)

    while len(queue) != 0:
        debug("----------------------------")
        node = queue.pop(0)
        status[node] = FOUND
        edges = graph[node]
        debug(queue)
        debug(status)
        debug(edges)
        for e in edges:
            if e == target:
                return True
            if status[e] == NOT_FOUND:
                status[e] = ENQUEUED
                queue.append(e)

    return False

if __name__ == "__main__":
    n, m = [int(x) for x in input().split()]

    g = [[] for i in range(n)]
    for i in range(m):
        u, e = [int(x) for x in input().split()]
        g[u].append(e)
        g[e].append(u)

    n = int(input())
    for i in range(n):
        s, d = [int(x) for x in input().split()]
        if bfs(g, s, d):
            print("yes")
        else:
            print("no")

Python: #!/usr/bin/env python3
import sys
input = lambda: sys.stdin.readline()[:-1]
sys.setrecursionlimit(10**8)

n,m=map(int,input().split())
G=[[]*n for i in range(n)]
color=[-1]*n
for i in range(m):
    v1,v2=map(int,input().split())
    G[v1].append(v2)
    G[v2].append(v1)


def dfs(v,c):
    color[v]=c
    for vi in G[v]:
        if color[vi]==-1:
            dfs(vi,i)


for i in range(n):
    if color[i]==-1:
        dfs(i,i)

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

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: import sys

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

def paint_col(adj, cols, i, col):
    nxt = [i]

    while nxt:
        u = nxt[-1]
        try:
            v = next(adj[u])
            if cols[v] == 0:
                cols[v] = col
                nxt.append(v)
        except StopIteration:
            nxt.pop()
            cols[u] = col

def solve():
    n, m = map(int, sys.stdin.readline().split())
    adj = [[] for i in range(n)]

    for i in range(m):
        s, t = map(int, sys.stdin.readline().split())
        adj[s].append(t)
        adj[t].append(s)

    cols = [0] * n
    col = 1
    adj = list(map(iter, adj))

    for i in range(n):
        if cols[i] == 0:
            paint_col(adj, cols, i, col)
            col += 1

    # debug(cols, locals())

    q = int(sys.stdin.readline())

    for i in range(q):
        s, t = map(int, sys.stdin.readline().split())

        if cols[s] == cols[t]:
            ans = 'yes'
        else:
            ans = 'no'

        print(ans)

if __name__ == '__main__':
    solve()

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 = tuple([] 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")