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A Java Template for Competitive Coding

sankalp srivastava
8 min readMay 11, 2020

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Many coders who like coding in Java for competitive coding have faced a “TLE” even though their logic and complexity are well within the bounds. The problem in those cases lies in our way of I/O. Using Scanner and System.out.println() in a code is much more convenient as compared to other methods but they are often too slow for large input and output.

The following is the template I use for competitive coding on platforms like Codechef and Codeforces:

Here the Reader class is a reference from: https://www.geeksforgeeks.org/fast-io-in-java-in-competitive-programming/

import java.io.*;
class Template
{
    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 Reader(String file_name) throws IOException 
        { 
            din = new DataInputStream(new FileInputStream(file_name)); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        }public String readLine() throws IOException 
        { 
            byte[] buf = new byte[64]; // line length 
            int cnt = 0, c; 
            while ((c = read()) != -1) 
            { 
                if (c == '\n') 
                    break; 
                buf[cnt++] = (byte) c; 
            } 
            return new String(buf, 0, cnt); 
        }public int nextInt() throws IOException 
        { 
            int ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do
            { 
                ret = ret * 10 + c - '0'; 
            }  while ((c = read()) >= '0' && c <= '9');if (neg) 
                return -ret; 
            return ret; 
        }public long nextLong() throws IOException 
        { 
            long ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
            if (neg) 
                return -ret; 
            return ret; 
        }public double nextDouble() throws IOException 
        { 
            double ret = 0, div = 1; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read();do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9');if (c == '.') 
            { 
                while ((c = read()) >= '0' && c <= '9') 
                { 
                    ret += (c - '0') / (div *= 10); 
                } 
            }if (neg) 
                return -ret; 
            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++]; 
        }public void close() throws IOException 
        { 
            if (din == null) 
                return; 
            din.close(); 
        } 
    } 
    static Reader sc=new Reader();
    static BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));
    public static void main(String args[])throws IOException
    {
        /*
         * For integer input: int n=inputInt();
         * For long input: long n=inputLong();
         * For double input: double n=inputDouble();
         * For String input: String s=inputString();
         * Logic goes here
         * For printing without space: print(a+""); where a is a variable of any datatype
         * For printing with space: printSp(a+""); where a is a variable of any datatype
         * For printing with new line: println(a+""); where a is a variable of any datatype
         */
        bw.flush();
        bw.close();
    }
    public static int inputInt()throws IOException
    {
        return sc.nextInt();
    }
    public static long inputLong()throws IOException
    {
        return sc.nextLong();
    }
    public static double inputDouble()throws IOException
    {
        return sc.nextDouble();
    }
    public static String inputString()throws IOException
    {
        return sc.readLine();
    }
    public static void print(String a)throws IOException
    {
        bw.write(a);
    }
    public static void printSp(String a)throws IOException
    {
        bw.write(a+" ");
    }
    public static void println(String a)throws IOException
    {
        bw.write(a+"\n");
    }
}

Running example:

The question ENGXOR (which was asked in Codechef March Challenge 2020) is a perfect example for the same.

Solution 1:

Using Scanner and System.out.println():

import java.util.*;
class MarchLong2
{
    public static void main(String args[])
    {
        HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();
        Scanner sc=new Scanner(System.in);
        int t=sc.nextInt();
        while(t-->0)
        {
            int n=sc.nextInt();
            int q=sc.nextInt();
            int e=0,o=0;
            for(int x=0;x<n;x++)
            {
                int ar=sc.nextInt();
                int a=0;
                if(map.containsKey(ar))
                {
                    a=map.get(ar);
                }
                else
                {
                    a=Integer.bitCount(ar);
                    map.put(ar,a);
                }
                if(a%2==0)
                {
                    e++;
                }
                else
                {
                    o++;
                }
            }
            while(q-->0)
            {
                int p=sc.nextInt();
                int a=0;
                if(map.containsKey(p))
                {
                    a=map.get(p);
                }
                else
                {
                    a=Integer.bitCount(p);
                    map.put(p,a);
                }
                if(a%2==0)
                {
                    System.out.println(e+" "+o);
                }
                else
                {
                    System.out.println(o+" "+e);
                }
            }
        }
    }
}

The program failed due to TLE.

Solution 2:

Using Fast I/O with System.out.println():

import java.io.DataInputStream; 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.io.InputStreamReader;
import java.util.HashMap;
class MarchLong2
{
    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 Reader(String file_name) throws IOException 
        { 
            din = new DataInputStream(new FileInputStream(file_name)); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        }public String readLine() throws IOException 
        { 
            byte[] buf = new byte[64]; // line length 
            int cnt = 0, c; 
            while ((c = read()) != -1) 
            { 
                if (c == '\n') 
                    break; 
                buf[cnt++] = (byte) c; 
            } 
            return new String(buf, 0, cnt); 
        }public int nextInt() throws IOException 
        { 
            int ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do
            { 
                ret = ret * 10 + c - '0'; 
            }  while ((c = read()) >= '0' && c <= '9');if (neg) 
                return -ret; 
            return ret; 
        }public long nextLong() throws IOException 
        { 
            long ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
            if (neg) 
                return -ret; 
            return ret; 
        }public double nextDouble() throws IOException 
        { 
            double ret = 0, div = 1; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read();do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9');if (c == '.') 
            { 
                while ((c = read()) >= '0' && c <= '9') 
                { 
                    ret += (c - '0') / (div *= 10); 
                } 
            }if (neg) 
                return -ret; 
            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++]; 
        }public void close() throws IOException 
        { 
            if (din == null) 
                return; 
            din.close(); 
        } 
    } 
    public static void main(String args[])throws IOException
    {
        /*int ans[]=new int[100001];
        for(int x=1;x<ans.length;x++)
        {
        ans[x]=countBits(x);
        }*/
        //initialize();
        HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();
        Reader sc=new Reader();
        int t=sc.nextInt();
        while(t-->0)
        {
            int n=sc.nextInt();
            int q=sc.nextInt();
            int e=0,o=0;
            for(int x=0;x<n;x++)
            {
                int ar=sc.nextInt();
                int a=0;
                if(map.containsKey(ar))
                {
                    a=map.get(ar);
                }
                else
                {
                    a=Integer.bitCount(ar);
                    map.put(ar,a);
                }
                if(a%2==0)
                {
                    e++;
                }
                else
                {
                    o++;
                }
            }
            while(q-->0)
            {
                int p=sc.nextInt();
                int a=0;
                if(map.containsKey(p))
                {
                    a=map.get(p);
                }
                else
                {
                    a=Integer.bitCount(p);
                    map.put(p,a);
                }
                if(a%2==0)
                {
                    System.out.println(e+" "+o);
                }
                else
                {
                    System.out.println(o+" "+e);
                }
            }
        }
    }
}

The program still fails due to TLE but the running time for accepted case is reduced.

Solution 3:

Using the template provided above(Fast Input + BufferedWriter):

import java.io.*;
import java.util.*;
class MarchLong2
{
    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 Reader(String file_name) throws IOException 
        { 
            din = new DataInputStream(new FileInputStream(file_name)); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        }public String readLine() throws IOException 
        { 
            byte[] buf = new byte[64]; // line length 
            int cnt = 0, c; 
            while ((c = read()) != -1) 
            { 
                if (c == '\n') 
                    break; 
                buf[cnt++] = (byte) c; 
            } 
            return new String(buf, 0, cnt); 
        }public int nextInt() throws IOException 
        { 
            int ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do
            { 
                ret = ret * 10 + c - '0'; 
            }  while ((c = read()) >= '0' && c <= '9');if (neg) 
                return -ret; 
            return ret; 
        }public long nextLong() throws IOException 
        { 
            long ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
            if (neg) 
                return -ret; 
            return ret; 
        }public double nextDouble() throws IOException 
        { 
            double ret = 0, div = 1; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read();do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9');if (c == '.') 
            { 
                while ((c = read()) >= '0' && c <= '9') 
                { 
                    ret += (c - '0') / (div *= 10); 
                } 
            }if (neg) 
                return -ret; 
            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++]; 
        }public void close() throws IOException 
        { 
            if (din == null) 
                return; 
            din.close(); 
        } 
    } 
    static Reader sc=new Reader();
    static BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));
    public static void main(String args[])throws IOException
    {
        HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();
        Reader sc=new Reader();
        int t=inputInt();
        while(t-->0)
        {
            int n=inputInt();
            int q=inputInt();
            int e=0,o=0;
            for(int x=0;x<n;x++)
            {
                int ar=inputInt();
                int a=0;
                if(map.containsKey(ar))
                {
                    a=map.get(ar);
                }
                else
                {
                    a=Integer.bitCount(ar);
                    map.put(ar,a);
                }
                if(a%2==0)
                {
                    e++;
                }
                else
                {
                    o++;
                }
            }
            while(q-->0)
            {
                int p=inputInt();
                int a=0;
                if(map.containsKey(p))
                {
                    a=map.get(p);
                }
                else
                {
                    a=Integer.bitCount(p);
                    map.put(p,a);
                }
                if(a%2==0)
                {
                    println(e+" "+o);
                }
                else
                {
                    println(o+" "+e);
                }
            }
        }
        bw.flush();
        bw.close();
    }
    public static int inputInt()throws IOException
    {
        return sc.nextInt();
    }
    public static long inputLong()throws IOException
    {
        return sc.nextLong();
    }
    public static double inputDouble()throws IOException
    {
        return sc.nextDouble();
    }
    public static String inputString()throws IOException
    {
        return sc.readLine();
    }
    public static void print(String a)throws IOException
    {
        bw.write(a);
    }
    public static void printSp(String a)throws IOException
    {
        bw.write(a+" ");
    }
    public static void println(String a)throws IOException
    {
        bw.write(a+"\n");
    }
}

The solution is now accepted.

NOTE: There may be faster methods for I/O in java but this method will work in almost all coding problems.

Codechef
Java
Template
Competitive Programming
Codeforces

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sankalp srivastava

Written by sankalp srivastava

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