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>

using namespace std;

const int N = 100000;
int A[N][N] = {{0}};
int n;

bool dfs(int s, int t) {
    if (A[s][t] == 1) {
        return true;
    }
    for (int i = 0; i < n; ++i) {
        if (i != t && A[s][i] != 0) {
            if (dfs(i, t)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int s, t;
        cin >> s >> t;
        A[s][t] = 1;
    }

    int q;
    cin >> q;
    for (int j = 0; j < q; ++j) {
        int x, y;
        cin >> x >> y;

        if (dfs(x, y)) {
            cout << "yes";
        } else {
            cout << "no";
        }
        cout << endl;
    }

    return 0;
}

C++: #include <iostream>#include <vector>#include <queue>static const int MAX=100000;using namespace std;vector<int> follow[MAX];int color[MAX];  //-1 represent No Visitedvoid bfs(int i,int c){    queue<int> Q;    Q.push(i);color[i]=c;    while(!Q.empty())    {        int p=Q.front();Q.pop();        for(int j=0;j<follow[p].size();j++)        {            if(color[follow[p][j]]!=-1) continue;            //else            Q.push(follow[p][j]); color[follow[p][j]]=color[p];        }    }}int main(){   int n,m;   cin>>n>>m;   for(int i=0;i<n;i++) color[i]=-1;   for(int i=0;i<m;i++)   {       int a,b;       cin>>a>>b;       follow[a].push_back(b);       follow[b].push_back(a);   }   int c=0;   for(int i=0;i<n;i++)   {       if(color[i]==-1)       {           bfs(i, c);           c++;       }   }   int order_num;cin>>order_num;   for(int i=0;i< order_num;i++)   {       int a,b;       cin>>a>>b;       if(color[a]==color[b]) cout<<"yes"<<endl;       else cout<<"no"<<endl;   }}

C++: #include <stdio.h>
#include <iostream>
#include <utility>
#include <algorithm>
#include <math.h>
#include <vector>
#include <list>
#define N 100000
using namespace std;
int n;
list<int> adj[N];
bool f[N] = {};

bool PathExists(int u, int v)
{
    f[u] = true;
    if (u == v)
        return true;
    while (!adj[u].empty())
    {
        if (!f[adj[u].front()] && PathExists(adj[u].front(), v))
            return true;
        adj[u].pop_front();
    }

    return false;
}

int main()
{
    int m, u, v, q;
    cin >> n >> m;

    for (int i = 0; i < m; i++)
    {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    cin >> q;
    for (int i = 0; i < q; i++)
    {
        cin >> u >> v;
        if (PathExists(u, v))
            printf("yes\n");
        else
            printf("no\n");
    }

    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_set>

using namespace std;

template<typename ISTREAM>
void readGraphListFromFriendInfo(ISTREAM& cin, vector< vector<int> >& friendGraphList) {
	size_t n;
	cin >> n;
	friendGraphList = vector< vector<int> >(n);
	size_t m;
	cin >> m;
	for (size_t i = 0; i != m; ++i) {
		size_t s,t;
		cin >> s >> t;
		friendGraphList.at(s).push_back(t);
		friendGraphList.at(t).push_back(s);
	}
	for (auto& v : friendGraphList)v.shrink_to_fit();
}

bool checkFriendAccesibility(const vector<vector<int>>& graphList, const int s, const int t, vector<bool>& isVisitList) {
	const size_t n = graphList.size();
	queue<int> nodeQueue;
	//vector<int> distanceList(n, -1);//
	fill(isVisitList.begin(), isVisitList.end(), false);
	nodeQueue.push(s);
	while (!nodeQueue.empty()) {
		const int id = nodeQueue.front();
		isVisitList.at(id).flip();//trueにする
		const auto& adjList = graphList.at(id);
		for (const auto& adjID : adjList) {
			if (isVisitList.at(adjID))continue;
			const vector<int>& idList = graphList.at(adjID);
			if ( find(idList.begin(), idList.end(), id ) == idList.end())continue;
			if (adjID == t)return true;
			nodeQueue.push(adjID);
		}
		nodeQueue.pop();
	}
	return false;
}

template<typename T>
void execute(T& cin) {
	vector< vector<int> > graphList;
	readGraphListFromFriendInfo(cin, graphList);
	vector<bool> isVisitList(graphList.size(), false);
	int q, s, t;
	cin >> q;
	for (int i = 0; i != q; ++i) {
		cin >> s >> t;
		cout << (checkFriendAccesibility(graphList, s, t, isVisitList) ? "yes" : "no") << endl;
	}
}

int main()
{

	execute(cin);

	return 0;
}