public class Solution {
/**
* @param n: An integer
* @param edges: a list of undirected edges
* @return: true if it's a valid tree, or false
*/
public boolean validTree(int n, int[][] edges) {
// condition check
if (n == 0) return false;
if (n - edges.length != 1) return false;
// 1. construct graph
Map<Integer, Set<Integer>> graph = new HashMap<>();
for (int i = 0; i < n; i++) {
graph.put(i, new HashSet<Integer>());
}
for (int[] e : edges) {
graph.get(e[0]).add(e[1]);
graph.get(e[1]).add(e[0]);
}
// 2. BFS
Queue<Integer> q = new ArrayDeque<>();
Set<Integer> visited = new HashSet<>();
q.offer(0);
visited.add(0);
while (!q.isEmpty()) {
int curr = q.poll();
for (int neighbor : graph.get(curr)) {
if (!visited.contains(neighbor)) {
q.offer(neighbor);
visited.add(neighbor);
}
}
}
// condition check
return visited.size() == n;
}
}
