[Link] https://www.acmicpc.net/problem/4803
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
static int max = 0, maxIdx = 0;
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
StringBuilder sb = new StringBuilder();
String[] line;
Node[] nodes;
boolean[] visit;
Node node;
int cntTot = 0;
int caseNum = 1;
while(true) {
line = getLine();
int n = toi(line[0]), m = toi(line[1]), treeNum = 0;
nodes = new Node[n];
for(int i = 0; i < n; i++) nodes[i] = new Node(i);
visit = new boolean[n];
if(n == 0 && m == 0) break;
for(int i = 0; i < m; i++) {
line = getLine();
int a = toi(line[0]) - 1, b = toi(line[1]) - 1;
nodes[a].list.add(b);
nodes[b].list.add(a);
}
Queue<Node> q = new LinkedList<>();
for(int i = 0; i < n; i++) {
if(visit[i]) continue;
q.clear();
q.add(nodes[i]);
treeNum += bfs(q, nodes, visit);
}
if(treeNum == 0) sb.append("Case " + caseNum + ": No trees.");
else if(treeNum == 1) sb.append("Case " + caseNum + ": There is one tree.");
else sb.append("Case " + caseNum + ": A forest of " + treeNum + " trees.");
caseNum++;
sb.append("\n");
}
print(sb);
}
static int bfs(Queue<Node> q, Node[] nodes, boolean[] visit) {
int vCnt = 0, adjCnt = 0;
while(!q.isEmpty()) {
Node cur = q.poll();
vCnt++;
adjCnt += cur.list.size();
if(visit[cur.idx]) continue;
visit[cur.idx] = true;
for(int e : cur.list) {
if(visit[e]) continue;
q.add(nodes[e]);
}
}
if(adjCnt == 2 * vCnt - 2) return 1;
return 0;
}
static class Node {
int idx;
ArrayList<Integer> list;
public Node(int idx) { this.idx = idx; list = new ArrayList<>(); }
}
static int toi(String s) { return Integer.parseInt(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}