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<iostream>
#include<vector>
#include<stack>
using namespace std;

static const int MAX = 100000;
static const int NIL = -1;

int n;
vector<int>G[MAX];
int color[MAX];

void dfs(int r, int c){
    stack<int> S;
    S.push(r);
    color[r] = c;
    while(!S.empty()){
        int u = S.top();S.pop();
        for(int i=0;i<G[u].size();i++){
            int v = G[u][i];
            if(color[v] == NIL){
                color[v] = c;
                S.push(v);
            }
        }
    }
}

void assignColor(){
    int id = 1;
    for(int i=0;i<n;i++)color[i] = NIL;
    for(int u=0;u<n;u++){
        if(color[u] == NIL)dfs(u,id++);
    }
}

int main(){
    int s,t,m,q;

    cin >> n >> m; // n = ノードの数 m = 辺の数 

    for(int i=0;i<m;i++){
        cin >> s >> t;
        G[s].push_back(t);
        G[t].push_back(s);
    }
    assignColor();
    
    cin >> q;

    for(int i=0;i<q;i++){
        cin >> s >> t;
        if(color[s] == color[t]){
            cout << "yes" << endl;
        }else
        {
            cout << "no" << endl;
        }
    }
    return 0;
}

C++: #ifndef ___Class_Union_Find
#define ___Class_Union_Find

#include <vector>
#include <utility>
#include <algorithm>

using namespace std;

class Union_Find
{
private:

    vector<int> data;
    
public:

    Union_Find(unsigned size_) : data(size_, -1) { }
    
    void unite(int x, int y);
    
    bool same(int x, int y);
    
    int root(int x);
};

void Union_Find::unite(int x, int y)
{
    x = root(x);
    y = root(y);
    
    if (x != y)
    {
        if (data[x] < data[y])
        {
            swap(x, y);
        }
        
        data[x] += data[y];
        data[y] = x;
    }
}

bool Union_Find::same(int x, int y)
{
    return root(x) == root(y);
}

int Union_Find::root(int x)
{
    return data[x] < 0 ? x : data[x] = root(data[x]);
}

#endif // ___Class_Union_Find


// ------ main ------ //

#include <cstdio>

int n, m, q, x, y;

int main()
{
    scanf("%d", &n);
    scanf("%d", &m);
    
    Union_Find u(n);
    
    for (int i = 0; i < m; i++)
    {
        scanf("%d", &x);
        scanf("%d", &y);
        
        u.unite(x, y);
    }
    
    scanf("%d", &q);
    
    for(int i = 0; i < q; i++)
    {
        scanf("%d", &x);
        scanf("%d", &y);
        
        printf("%s\n", u.same(x, y) ? "yes" : "no");
    }
    
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define rep(i, a, b) for (int i = (a); i < (int)(b); i++)
#define rrep(i, a, b) for (int i = (a); i >= (int)(b); i--)
#define all(x) (x).begin(), (x).end()
using i32 = int32_t;
using i64 = int64_t;
using f32 = float;
using f64 = double;
using P   = pair<int, int>;

template <class T>
bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    } else {
        return false;
    }
}
template <class T>
bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    } else {
        return false;
    }
}

template <class T>
void dump_vec(const vector<T>& v) {
    auto len = v.size();
    rep(i, 0, len) {
        cout << v[i] << (i == (int)len - 1 ? "\n" : " ");
    }
}

struct FastIO {
    FastIO() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(20);
    }
} FASTIO;

//---------------------------------------------------------------------------------------------------

struct UnionFind {
    vector<int> _ids; // 添字iが属する集合のID

    UnionFind(int n) {
        _ids.assign(n, -1);
    }

    int root(int x) {
        const auto rx               = _ids[x];
        return rx < 0 ? x : _ids[x] = root(rx);
    }

    // 要素xとyは同じ連結成分に属するか？
    bool connected(int x, int y) {
        return root(x) == root(y);
    }

    // 要素xが属する集合の要素数
    int size(int x) {
        return -_ids[root(x)];
    }

    // 要素xとyを連結
    bool unite(int x, int y) {
        auto rx = root(x), ry = root(y);
        if (rx == ry) return false;

        if (_ids[rx] > _ids[ry]) swap(rx, ry);
        _ids[rx] += _ids[ry];
        _ids[ry] = rx;
        return true;
    }
};
//---------------------------------------------------------------------------------------------------

signed main() {
    int N, Q;
    cin >> N >> Q;
    UnionFind uf(N);
    rep(i, 0, Q) {
        int a, b;
        cin >> a >> b;
        uf.unite(a, b);
    }
    cin >> Q;
    rep(i, 0, Q) {
        int a, b;
        cin >> a >> b;
        cout << (uf.connected(a, b) ? "yes" : "no") << "\n";
    }
}