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: # ALDS1_11_D Connected Components
import sys
import queue


sys.setrecursionlimit(1000000)

def check(adj, foot_print):
    n = len(foot_print)
    que = queue.Queue()
    num = 0
    for i in range(n):
        if foot_print[i] == 0:
            num += 1
            que.put(i)
            foot_print[i] = num
            bfs(adj, que, foot_print, num)


def bfs(adj, que, foot_print, num):
    if not que.empty():
        now = que.get()
        for i in adj[now]:
            if foot_print[i] == 0:
                foot_print[i] = num
                que.put(i)
        bfs(adj, que, foot_print, num)
    else:
        return


def main():
    n, m = map(int, sys.stdin.readline().strip().split())
    adj_list = [[] for _ in range(n)]
    for i in range(m):
        s, t = map(int, sys.stdin.readline().strip().split())
        adj_list[s].append(t)
        adj_list[t].append(s)

    foot_print = [0] * n
    check(adj_list, foot_print)

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


if __name__ == '__main__':
    main()

Python: n, m = map(int, input().split())
rootList = [-1] * n

def getRoot(x):
    if rootList[x] < 0:
        return x
    return getRoot(rootList[x])


def setSameRoot(x, y):
    x = getRoot(x)
    y = getRoot(y)
    if x != y:
        G[x], G[y] = min(x, y), min(x, y)

for i in range(m):
    s, t = map(int, input().split())
    setSameRoot(s, t)
q = int(input())
for i in range(q):
    s, t = map(int, input().split())
    print("yes" if getRoot(s) == getRoot(t) else "no")

Python: #!/usr/bin/env python
# -*- coding: utf-8 -*-
 
import sys
 
 
def assign_color():
    _color = 1
    for m in range(vertices_num):
        if vertices_status_list[m] == -1:
            graph_dfs(m, _color)
            _color += 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
 
 
def solve():
    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")
    return vertices_status_list
 
 
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
    ans = solve()

Python: def connect(o,s,t):
    global ct
    if color[s]!="white" or ct!=1:
        return
    if fr[o][t]==t:
        ct+=1
    color[s]="grey"
    for i in fr[s]:
        if i==-1:
            continue
        elif i==t or ct!=0:
             ct+=1
             break
        else:
            fr[o][i]=i
            fr[i][o]=s
            connect(o,i,t)
            
n,m=map(int,raw_input().split())
fr=[[-1]*n for i in xrange(n)]
for i in xrange(m):
    s,t=map(int,raw_input().split())
    fr[s][t]=t
    fr[t][s]=s
q=input()
for i in xrange(q):
    ct=0
    color=["white"]*n
    s,t=map(int,raw_input().split())
    connect(s,s,t)
    if ct==0:
        print('no')
    else:
        print('yes')
        fr[s][t]=t
        fr[t][s]=s

Python: #!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys


def assign_color():
    _color = 1
    for m in range(vertices_num):
        if vertices_status_list[m] == -1:
            graph_dfs(m, _color)
            _color += 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")