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 <bits/stdc++.h>

using namespace std;

#define rep(i, n) for(int i = 0; i < (int)n; ++i)
#define FOR(i, a, b) for(int i = a; i < (int)b; ++i)
#define rrep(i, n) for(int i = ((int)n - 1); i >= 0; --i)

typedef long long ll;
typedef long double ld;

const int Inf = 1e9;
const double EPS = 1e-9;
const int MOD = 1e9 + 7;

class UnionFind {
    public:
        vector<int> rank, p, size;

        UnionFind() {}
        UnionFind(int s) {
            rank.resize(s, 0);
            p.resize(s, 0);
            size.resize(s, 0);
            rep (i, s) init(i);
        }

        void init(int x) {
            p[x] = x;
            rank[x] = 0;
            size[x] = 1;
        }

        bool isSame(int x, int y) {
            return root(x) == root(y);
        }

        void unite(int x, int y) {
            if (isSame(x, y)) return;
            link(root(x), root(y));
        }

        void link(int x, int y) {
            if (rank[x] > rank[y]) {
                p[y] = x;
                size[x] += size[y];
            } else {
                p[x] = y;
                size[y] += size[x];
                if (rank[x] == rank[y]) {
                    rank[y]++;
                }
            }
        }

        int root(int x) {
            if (x != p[x]) {
                p[x] = root(p[x]);
            }
            return p[x];
        }

        int getSize(int x) {
            return size[root(x)];
        }
};

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(0);
    int n, m, q;
    cin >> n >> m;
    UnionFind uf = UnionFind(n);
    rep (i, m) {
        int s, t;
        cin >> s >> t;
        uf.unite(s, t);
    }
    cin >> q;
    rep (i, q) {
        int s, t;
        cin >> s >> t;
        if (uf.isSame(s, t)) cout << "yes" << endl;
        else cout << "no" << endl;
    }
    
    return 0;
}

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

  cin >> n >> m;

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

#define NIL -1

void dfs(int r, int id, vector<vector<int>> &G, vector<int> &color) {
    stack<int> S;
    S.push(r);

    color[r] = id;
    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] = id;
                S.push(v);
            }
        }
    }
}

void assignColor(vector<vector<int>> &G, vector<int> &color) {
    int id = 1;

    for (int i = 0; i < G.size(); i++)
        color[i] = NIL;

    for (int u = 0; u < G.size(); u++) {
        if (color[u] == NIL) {
            dfs(u, id, G, color);
            id++;
        }
    }
}

int main() {
    int n, m;
    cin >> n >> m;

    vector<vector<int>> G(n);
    vector<int> color(n);

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

    // グループ分け
    assignColor(G, color);

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

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1LL << 60;
const ll MOD = 1000000007;

int N, M;
int cnt = 0;
vector<vector<int>> G;

vector<int> seen;
void dfs(int v) {
    seen[v] = cnt;

    for (auto nv : G[v]) {
        if (seen[nv] != -1) continue;

        dfs(nv);
    }
}

int main() {
    cin >> N >> M;
    G.resize(N);
    seen.assign(N, -1);
    for (int i = 0; i < M; i++) {
        int a, b; cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    for (int v = 0; v < N; v++) {
        if (seen[v] != -1) continue;

        dfs(v);
        cnt++;
    }

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