#include <cstdio>
#include <vector>
using namespace std;
int n, m;
vector <int> graph[10100];
bool visited[10100];
void dfs(int node) {
if(visited[node]) {
return;
} else {
visited[node] = true;
for (int neighbour:graph[node]) {
dfs(neighbour);
}
}
}
int main() {
scanf("%d%d", &n, &m);
for (int i = 0;i < m;i++) {
int u, v;
scanf("%d%d", &u, &v);
u--;
v--;
graph[u].push_back(v);
graph[v].push_back(u);
}
if (m != n-1) {
printf("NO");
return 0;
}
dfs(0);
int b = 0;
for (int i = 0;i < 10100;i++) {
if (visited[i]) {
b++;
}
}
if (b == n) {
printf("YES");
} else {
printf("NO");
}
return 0;
}
Replies to PT07Y
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