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100000620-01.cpp
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100000620-01.cpp
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#include <cstdio>
#include <vector>
#include <queue>
#define MAXN 1005
using namespace std;
vector<int> adj_list[MAXN];
bool in_queue[MAXN] = {};
void bfs(int n)
{
queue<int> q;
q.push(n);
in_queue[n] = true;
while (q.size())
{
int front = q.front(); q.pop();
for (int i = 0; i < adj_list[front].size(); i++)
{
int v = adj_list[front][i];
if (v != 0)
{
q.push(v);
in_queue[v] = true;
adj_list[front][i] = 0;
}
}
}
}
bool is_connected_graph(int size)
{
bfs(1);
for (int i = 1; i <= size; i++)
if (in_queue[i] == false)
return false;
return true;
}
void reset(int size)
{
for (int i = 1; i <= size; i++)
{
adj_list[i].clear();
in_queue[i] = false;
}
}
int main()
{
int n, m;
while (scanf("%d", &n) == 1 && n != 0)
{
scanf("%d", &m);
int a, b;
for (int i = 0; i < m; i++)
{
scanf("%d %d", &a, &b);
adj_list[a].push_back(b);
adj_list[b].push_back(a);
}
printf(is_connected_graph(n) ? "YES\n" : "NO\n");
reset(n);
}
return 0;
}