Time Lapse :3min 4sec

1862.java

import java.io.*;

public class Main {
    public static int n, m, i, a, b, ans = 0;
    public static int[] g = new int[50001];
    public static boolean[] v = new boolean[50001];
    public static Reader r = new Reader();
    public static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    public static void main(String[] args) throws Exception {
        n = r.nextInt();
        m = r.nextInt();
        for(i = 1; i <= n; ++i)
            g[i] = i;
        for(i = 0; i < m; ++i) {
            a = getG(r.nextInt());
            b = getG(r.nextInt());
            g[a] = g[b] = Math.min(a, b);
        }
        for(i = 1; i <= n; ++i)
            gC(i);
        System.out.println(ans);
    }
    public static void gC(int n) {
        if(v[n]) return;
        v[n] = true;
        if(g[n] != n) gC(g[n]);
        else ++ans;
    }

    public static int getG(int n) {
        return n == g[n] ? n : (g[n] = getG(g[n]));
    }

    static class Reader {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            do {
                ret = (ret<<3) + (ret<<1)  + (c & 0b1111);
            } while ((c = read()) >= '0' && c <= '9');

            return ret;
        }
        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

    }
}