bool isTree(int parent, int node, vector<vector<int> >& adj, vector<bool>& visited) {

visited[node] = true;

for(int i = 0; i < (int) adj[node].size(); ++i) {

if(adj[node][i] != parent) {

int child = adj[node][i];

if(visited[child]) {

return false;

}

if(!isTree(node, child, adj, visited)) {

return false;

}

}

}

return true;

}

bool validTree(int n, vector<pair<int, int>>& edges) {

vector<vector<int> > adj (n, vector<int>());

for(int i = 0; i < edges.size(); ++i) {

int u = edges[i].first;

int v = edges[i].second;

adj[u].push_back(v);

adj[v].push_back(u);

}

vector<bool> visited(n, false);

bool isValidTree = isTree(-1, 0, adj, visited);

if(isValidTree) for(int i = 0; i < n; ++i) {

if(!visited[i]) {

return false;

}

}

return isValidTree;

}