Java for Competitive Programming

While C++ is the most popular language in competitive programming, Java is a very strong alternative. It features robust built-in libraries, automatic memory management, and excellent tools for big integer arithmetic and decimal precision.

Fast I/O in Java

Standard Scanner and System.out.println are slow and can cause Time Limit Exceeded (TLE) errors. Using a custom fast reader class is crucial.

import java.io.*;
import java.util.*;

public class Main {
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    public static void main(String[] args) {
        FastReader in = new FastReader();
        PrintWriter out = new PrintWriter(new BufferedOutputStream(System.out));
        
        // Solve the problem here
        int n = in.nextInt();
        out.println(n);
        
        out.close();
    }
}

Useful Java Libraries

• BigInteger and BigDecimal: Perfect for arithmetic that exceeds 64-bit limits.
• TreeMap and TreeSet: Highly functional red-black tree implementations.