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 <cstdio>
#include <algorithm>
#include <unordered_set>

int main(){
    int n;
    int m;
    std::scanf("%d", &n);
    std::scanf("%d", &m);
    static std::unordered_set<int> relations[100000];
    int rCount = 0;
    for(int i = 0; i < m; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        bool find = false;
        for(int j = 0; j < rCount; ++j){
            if(relations[j].find(s) != relations[j].end()){
                if(relations[j].find(t) == relations[j].end()){
                    relations[j].insert(t);
                }
                find = true;
                break;
            } else if(relations[j].find(t) != relations[j].end()){
                if(relations[j].find(s) == relations[j].end()){
                    relations[j].insert(s);
                }
                find = true;
                break;
            }
        }
        if(find == false){
            relations[rCount].insert(s);
            relations[rCount].insert(t);
            ++rCount;
        }
    }
    int q;
    std::scanf("%d", &q);
    for(int i = 0; i < q; ++i){
        int s;
        int t;
        std::scanf("%d", &s);
        std::scanf("%d", &t);
        bool find = false;
        for(int j = 0; j < rCount; ++j){
            if(relations[j].find(s) != relations[j].end() && relations[j].find(t) != relations[j].end()){
                find = true;
                break;
            }
        }
        if(find){
            std::printf("yes\n");
        } else {
            std::printf("no\n");
        }
    }

    return 0;
}

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

const int MAX = 100000;
vector<int> G[MAX];

class DisjointSet{
public:
    vector<int> rank, parent;
    DisjointSet();
    DisjointSet(int size){
        rank.resize(size,0);
        parent.resize(size,0);
        for (int i=0; i<size; i++) {
            makeSet(i);
        }
    }

//    bool same(int u,int v){
//        if (parent[u] == parent[v]) {
//            return true;
//        }else{
//            return false;
//        }
//    }
    bool same(int u,int v){
        int x = findSet(u); int y= findSet(v);
        return x==y;
    }
    
    void unite(int u,int v){
        int x = findSet(u);int y= findSet(v);
        if(rank[x]<rank[y]){
            parent[x] = y;
        }else{
            parent[y] = x;
            if(rank[x]==rank[y]){
                rank[x]++;
            }
        }
    }
    // ????????????????????????
    int findSet(int u){
        
        if(u!=parent[u])
            parent[u] = findSet(parent[u]);
        
        return parent[u];
    }
private:
    void makeSet(int i){
        rank[i] = 0;
        parent[i] = i;
    }
};
    
int main(int argc, const char * argv[]) {
    
    int n,m;
    cin >> n >> m;
    DisjointSet ds(n);
    
    for(int i=0;i<m;i++){
        int s,t;
        cin >> s >> t;
        ds.unite(s, t);
    }
    int q;
    cin >> q;
    for(int i=0;i<q;i++){
        int s,t;
        cin >> s >> t;
        if(ds.same(s, t)) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;


int n;

string *color;

queue<int> q;

int *ans;

vector<int> g[10000];


void bfs(int x){
  color[x] = "gray";
  q.push(x);


  while(q.size() != 0){
    int u = q.front();
    q.pop();

    for(int i = 0; i < g[u].size(); i++){
      int v = g[u][i];
      if(color[v] == "white"){
        color[v] = "gray";
        q.push(v);
      }
    }

    color[u] = "black";
    ans[u] = x;


  }
  cout << x << endl;
  return;
}


int main(){

  cin >> n;

  color = new string[n];

  ans = new int[n];

  int m;

  cin >> m;


  int a, b;


  for(int i = 0; i < m; i++){
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }


  for(int i = 0; i < n; i++){
    color[i] = "white";
  }


  for(int j = 0; j < n; j++){
    if(color[j] == "white"){
      bfs(j);
    }
  }

  int q;

  cin >> q;

  for(int i = 0; i < q; i++){
    cin >> a >> b;
    if(ans[a] == ans[b]){
      cout << "yes" << endl;
    }
    else{
      cout << "no" << endl;
    }
  }

  return 0;
}

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

bool isReachable(int k, int l, vector<vector<int> > node) {
	int n=(int)node.size();
	int i;
	int m;
	queue<int> qnode;
	vector<int> visited;
	visited.resize(n);
	for(i=0; i<n; ++i) {
		visited[i]=0;
	}
	visited[k]=1;
	qnode.push(k);
	while(!qnode.empty()) {
		m=qnode.front();
		for(i=0; i<(int)node[m].size(); ++i) {
			if(node[m][i]==l) {
				return true;
			} else {
				if(visited[node[m][i]]==0) {
					qnode.push(node[m][i]);
					visited[node[m][i]]=1;
				}
			}
		}
		qnode.pop();
	}
	return false;
}

int main() {
	int m,n,k,l;
	int q;
	int i;
	vector<vector<int> > node;
	scanf("%d%d",&n,&m);
	node.resize(n);
	for(i=0; i<m; ++i) {
		scanf("%d%d",&k,&l);
		node[k].push_back(l);
		node[l].push_back(k);
	}
	scanf("%d",&q);
	for(i=0; i<q; ++i) {
		scanf("%d%d",&k,&l);
		printf((isReachable(k,l,node)?"yes\n":"no\n"));
	}
	return 0;
}