Kattis-Problems/SortOfSorted2.java at master · gsyndromes/Kattis-Problems · GitHub

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import java.util.*;
import java.io.BufferedReader;
import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class SortOfSorted2 {

    public static String[] mergeSort(String[] arr) {
        // if array length is 1 -> return arr
        if (arr.length == 0) {
            return arr;
        }

        String[] firstHalf = Arrays.copyOfRange(arr, 0, (arr.length / 2) + 1);
        String[] secondHalf = Arrays.copyOfRange(arr, (arr.length / 2) + 1, arr.length);
        String[] newFirstHalf = mergeSort(firstHalf);
        String[] newSecondHalf = mergeSort(secondHalf);

       // merge two sorted into one
        String[] merged = new String[arr.length];
        int a = 0;
        int b = 0;
        int mergePointer = 0;
        while ((a < firstHalf.length) && ( b < secondHalf.length)) {
            int temp = newFirstHalf[a].charAt(0) - newSecondHalf[b].charAt(0);
            if (temp < 0) {
                merged[mergePointer] = newFirstHalf[a];
                mergePointer++;
                a++;
            } else if (temp > 0) {
                merged[mergePointer] = newSecondHalf[b];
                mergePointer++;
                b++;
            } else {
                int temp2 = newFirstHalf[a].charAt(1) - newSecondHalf[b].charAt(1);
                if (temp2 <= 0) {
                    merged[mergePointer] = newFirstHalf[a];
                    mergePointer++;
                    a++;
                } else {
                    merged[mergePointer] = newSecondHalf[b];
                    mergePointer++;
                    b++;
            }
        }

        if (a == newFirstHalf.length) {
            for (int i = mergePointer; i < merged.length; i++) {
                merged[i] = newSecondHalf[b];
                b++;
            }
        }
        if (b == newSecondHalf.length) {
            for (int i = mergePointer; i < merged.length; i++) {
                merged[i] = newSecondHalf[a];
                a++;
            }
        }

    }
    return merged;
}


    public static void main(String[] args){
        FastIO fio = new FastIO();
        int n = fio.nextInt();

        while (n != 0) {
            String[] studentList = new String[n];
            for(int i = 0; i < n; i++){
                studentList[i] = (fio.nextLine());
            }
           String[] mergedStudentList = mergeSort(studentList);

            for (int i = 0; i < n; i++) {
                fio.println(mergedStudentList[i]);
            }
            n = fio.nextInt();
            if (n != 0){
                fio.println();
            }


        }

        fio.close();

    }

}


/**
 * Fast I/O
 * @source https://www.geeksforgeeks.org/fast-io-in-java-in-competitive-programming/
 */
class FastIO extends PrintWriter
{
    BufferedReader br;
    StringTokenizer st;

    public FastIO()
    {
        super(new BufferedOutputStream(System.out));
        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;
    }
}