poj2524(并查集)

点击打开题目链接

大意：多组数据。每组数据中，n个学生，每个学生信最多一种教。给出m对学生信息，每对中两个学生信的教一样。

求这n个学生信教种数最多有多少。

思路：并查集，基础练手题

代码如下：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

class Reader {
	static BufferedReader reader;
	static StringTokenizer tokenizer;

	static void init(InputStream input) {
		reader = new BufferedReader(new InputStreamReader(input));
		tokenizer = new StringTokenizer("");
	}

	static String next() throws IOException {
		while (!tokenizer.hasMoreTokens()) {
			tokenizer = new StringTokenizer(reader.readLine());
		}
		return tokenizer.nextToken();
	}

	static int nextInt() throws IOException {
		return Integer.parseInt(next());
	}
}

public class Main {

	/**
	 * @param args
	 */
	static int ans, n, m, pa, pb, u, v, casenum;
	static int p[], rank[];

	private static int father(int u) {
		if (u == p[u])
			return u;
		p[u] = father(p[u]);
		return p[u];
	}

	private static void merge(int a, int b) {
		pa = father(a);
		pb = father(b);
		if (pa != pb) {
			if (rank[pa] < rank[pb])
				p[pa] = pb;
			else
				p[pb] = pa;
			if (rank[pa] == rank[pb])
				rank[pa]++;
		}
	}

	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		Reader.init(System.in);
		p = new int[50001];
		rank = new int[50001];
		n = Reader.nextInt();
		m = Reader.nextInt();
		casenum = 0;
		while ((n != 0) || (m != 0)) {
			casenum++;
			for (int i = 1; i <= n; i++) {
				p[i] = i;
				rank[i] = 1;
			}
			for (int i = 1; i <= m; i++) {
				u = Reader.nextInt();
				v = Reader.nextInt();
				merge(u, v);
			}
			ans = 0;
			for (int i = 1; i <= n; i++)
				if (p[i] == i)
					ans++;
			System.out.println("Case " + casenum + ": " + ans);
			n = Reader.nextInt();
			m = Reader.nextInt();
		}
	}

}