Question

JAVA - Natural Quick Sort .txt and Return

-----------------------------------------------------------------------------

The program should input a .txt file like below and must use a Quick sort Algorithm

================

6 10

4 19 10 12 8 6

0 1 2

3

================

The first number "6" represents the index of the element to return after sort

the second number on the top "10" represents the number of elements or size of array.

The following numbers and lines are the elements that need to go into the array and be sorted.

-----------------------------------------------------------------------------

It should then:

1) Sort using the natural variant of quick sort algorithm and return the "6"th element

the "6" comes from the text file and should work with whatever number the text file has as long as its less than or equal to the second number, in this case "10".

Example Output given above .txt file:

Quicksort finds 8.

Answer 1

package sort;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.util.Scanner;

public class ReadFromFileAndSort {

static int index;

private static int[] readFromFile(String filename) throws IOException {

File file = new File(filename); //make new files

String res="";

Scanner sc = null;

String firstLine="";

int size=0;

int ar[]=new int[0];

int i=0;

try {

sc = new Scanner(file); //read file using scanner

while (sc.hasNext()) {

firstLine=sc.nextLine();

index=Integer.parseInt(firstLine.split(" ")[0]);

size=Integer.parseInt(firstLine.split(" ")[1]);

break;

}

ar=new int[size];

while(sc.hasNext()){

String temp[]=sc.nextLine().split(" ");

for(int j=0;j<temp.length;j++){

ar[i++]=Integer.parseInt(temp[j]);

}

}

} catch (FileNotFoundException e) {

System.err.println(e.getMessage());

} finally {

if (sc != null) {

sc.close();

}

}

return ar;

}

public static int part(int ar[], int l, int h)

{

int p = ar[l]; //to first element for array as pivote

int j=h; //j as highest

int i = (h+1); //after highest index

while (j>l) //run loop j greater the low

{

if (ar[j]>= p) { //if jth element greater then p

i--; //swap ith and jth element

int t = ar[i];

ar[i] = ar[j];

ar[j] = t;

}

j--; //go to lower element

}

int t = ar[i-1]; //swap pivot if it is not at right place

ar[i-1] = ar[l];

ar[l] = t;

return i-1;

}

public static void sort(int ar[], int l, int h)

{

if (l < h)

{

//using divide and concor

int pi = part(ar, l, h); //find pivote index

sort(ar, l, pi-1); //sort array before pivot

sort(ar, pi+1, h); //after pivot

}

}

public static void main(String[] args) throws IOException {

String file="/Users/snehkuma/Documents/HomeworkLib/HomeworkLib/Sort.txt";

int ar[]=readFromFile(file);

sort(ar, 0, ar.length-1);

System.out.print(ar[index]+" ");

}

}