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")
		}
	}
}

C++: #include <cmath>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <sstream>
#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;
 
struct node {
    int id;
    vector<int> rel;
};

struct memo {
	int a, b;
	bool val;
	bool operator==(memo m){
		return (this->a == m.a && this->b == m.b) || (this->a == m.b && this->b == m.a);
	}
};
 
int n, m, q;
node* nodes;
vector<memo> ms;

bool canReach(int s, int d, bool* h){
    h[s] = true;
	if(s==d) return true;
	
	memo nm;
	nm.a = s;
	nm.b = d;
	
	vector<memo>::iterator it = find(ms.begin(), ms.end(), nm);
	if(it != ms.end()) return (*it).val;
	
    for(int i = 0; i < nodes[s].rel.size(); i++){
		if(!h[nodes[s].rel[i]] && canReach(nodes[s].rel[i], d, h)){
			nm.val = true;
			ms.push_back(nm);
			return true;
        }
    }
	
	nm.val = false;
	ms.push_back(nm);
    return false;
}
 
int main() {
    scanf("%d %d", &n, &m);
     
    nodes = new node[n];
    for(int i = 0; i < n; i++){
        nodes[i].id = i;
    }
    while(m--){
        int l, r;
        scanf("%d %d", &l, &r);
        nodes[l].rel.push_back(r);
        nodes[r].rel.push_back(l);
    }
     
    scanf("%d", &q);
    while(q--){
        int l, r;
        scanf("%d %d", &l, &r);
         
        bool *h = new bool[n];
        for(int i = 0; i < n; i++){
            h[i] = false;
        }
        printf("%s\n", canReach(l, r, h) ? "yes" : "no");
        delete[] h;
    }
    return 0;
}

C++: def dfs(s):
    global t
    if s == t:
        return True
    DP[s]=1
    for i in F[s]:
        if not DP[i]:
            if dfs(i):
                return True
    return False
    
n,m = [int(i) for i in input().split()]
F = [{}]*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
    s,t = [int(i) for i in input().split()]
    if dfs(s):
        print("yes")
    else:
        print("no")

C++: #include <iostream>
#include <vector>
using namespace std;

struct node {
    int to;
    node *next;
};

node *adj[100000], fm[200000];
int g[100000];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, i;
    cin>>n>>m;
    m+=m;
    int s, t;
    i=0;
    while(i<m) {
        cin>>s>>t;
        fm[i].to=t;
        fm[i].next=adj[s];
        adj[s]=&fm[i];
        i++;
        fm[i].to=s;
        fm[i].next=adj[t];
        adj[t]=&fm[i];
        i++;
    }
    int group=1;
    vector<int> st;
    st.reserve(n);
    for(i=0; i<n; i++) {
        if(g[i]) continue;
        g[i]=group;
        st.push_back(i);
        while(!st.empty()) {
            node *p=adj[st.back()];
            g[st.back()]=group;
            st.pop_back();
            while(p) {
                if(g[p->to]==0) st.push_back(p->to);
                p=p->next;
            }
        }
        group++;
    }
    cin>>n;
    for(int i=0; i<n; i++) {
        cin>>s>>t;
        if(g[s]==g[t]) cout<<"yes\n";
        else cout<<"no\n";
    }
    return 0;
}

C++: #define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#include <list>

long long int INF = 1e18;
using namespace std;

typedef pair<long long int, long long int> P;

#define MAX_N 200000

int par[MAX_N];
int rnk[MAX_N];

// 初期化
void init(int n){
	for(int i = 0; i < n; i++){
		par[i] = i;
		rnk[i] = 0;
	}
}

// x の親を返す
int find(int x){
	if(par[x] == x){
		return x;
	}
	return par[x] = find(par[x]);
}

// x と y を併合する
void unite(int x, int y){
	int x_par = find(x);
	int y_par = find(y);
	if(x_par == y_par){
		return;
	}
	
	if(rnk[x_par] < rnk[y_par]){
		par[x_par] = y_par;
	}else{
		par[y_par] = x_par;
		if(rnk[x_par] == rnk[y_par]){
			rnk[x_par]++;
		}
	}
}

// x, y が同じグループか判定
bool same(int x, int y){
	return (find(x) == find(y));
}

int main(){
	
	int n, m;
	cin >> n >> m;
	
	init(n);
	
	for(int i = 0; i < m; i++){
		int x, y;
		cin >> x >> y;
		unite(x, y);
	}
	
	int q;
	cin >> q;
	
	for(int i = 0; i < q; i++){
		int x, y;
		cin >> x >> y;
		if(same(x, y)){
			cout << "yes" << endl;
		}else{
			cout << "no" << endl;
		}
	}
	
	return 0;
}