Question

Java QuickSort Methods

Asked by: elliottbenzle

I am trying to get this java to:

(1) Read numbers from a file,
(2) Input into an array,
(3) Apply quickSort/partition method to the array, and
(4) Print out (only) the sorted array to the screen.

    This is my current output below. Thanks to anyone that can help me get this program running with correct output.

//user input is the, "text.txt"
Name of file with array: text.txt

[4, 0, 0, 0, 0]
Exception in thread "main" [4, 8, 0, 0, 0]
[4, 8, 6, 0, 0]
[4, 8, 6, 10, 0]
[4, 8, 6, 10, 2]
java.util.NoSuchElementException
      at java.util.Scanner.throwFor(Unknown Source)
      at java.util.Scanner.next(Unknown Source)
      at ss.testScan1(ss.java:26)
      at ss.main(ss.java:10)

import java.io.*;
import java.io.File;
import java.util.Scanner;
 
public class ss {
	public static void main(String[] args) throws IOException {
		System.out.print("Name of file with array: ");
		Scanner readIn = new Scanner(System.in);
		String input = readIn.nextLine();
		testScan1(input);
	}
 
	public static void testScan1(String filename) {
		File file = new File(filename);
		Scanner scan;
		int[] array;
		try {
			array = new int[5];
			scan = new Scanner(file);
		} catch (java.io.FileNotFoundException e) {
			System.out.println("couldn't open. file not found ");
			return;
		}
		while (scan.hasNext()) {
			for (int i = 0; i <= file.length(); ++i) {
				array[i] = Integer.parseInt(scan.next());
				System.out.println(java.util.Arrays.toString(array));
				//for (int j = 0; j < array.length; ++j)
					//System.out.println(array[i] + " ");
			}
		}
	}
 
	int partition(int[] arr, int left, int right) {
		int i = left;
		int j = right;
		int tmp;
		int pivot = arr[(left + right) / 2];
		while (i <= j) {
			while (arr[i] < pivot)
				i++;
			while (arr[j] > pivot)
				j--;
			if (i <= j) {
				tmp = arr[i];
				arr[i] = arr[j];
				arr[j] = tmp;
				i++;
				j--;
			}
		}
		return i;
	}
 
	void quickSort(int[] arr, int left, int right) {
		int index = partition(arr, left, right);
		if (left < (index - 1)) {
			;
		}
		quickSort(arr, left, index - 1);
		if (index < right) {
			quickSort(arr, index, right);
		}
	}
}

                                  
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Asked On
2009-11-05 at 16:53:42ID24876716
Tags

Java

,

beginner

,

quicksort

Topics

Java Programming Language

,

New to Java Programming

Participating Experts
1
Points
500
Comments
4

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Answers

 

by: jb1devPosted on 2009-11-05 at 17:15:22ID: 25755921

You're using the Scanner incorrectly. What's the format of your input file?
Try this instead around line 36.

        int i = 0;
        while (scan.hasNext()) {
            array[i] = Integer.parseInt(scan.next());
            i++;
        }

 

by: jb1devPosted on 2009-11-05 at 17:16:49ID: 25755927

Err I mean around line 24. Where you are calling scan.hasNext() and scan.next().

 

by: elliottbenzlePosted on 2009-11-05 at 17:21:40ID: 25755942

Ok, made the change but am getting "at ss.quickSort(ss.java:66)" when I try an run it after inputing the file name

import java.io.*;
import java.io.File;
import java.util.Scanner; 
public class ss {
	public static void main(String[] args) throws IOException {
		System.out.print("Name of file with array: ");
		Scanner readIn = new Scanner(System.in);
		String input = readIn.nextLine();
		testScan1(input);
		
	} 
	public static void testScan1(String filename) {
		File file = new File(filename);
		Scanner scan;
		int[] array;
		try {
			array = new int[5];
			scan = new Scanner(file);
		} catch (java.io.FileNotFoundException e) {
			System.out.println("couldn't open. file not found ");
			return;
		}
		int i =0;
		while (scan.hasNext()) {
			//for (i = 0; i <= file.length(); ++i) 
				array[i] = Integer.parseInt(scan.next());
				i++;}
				quickSort(array, 0, array.length-1);
			partition(array, 0, array.length-1);
			
				//System.out.println(java.util.Arrays.toString(array));
				for (int j = 0; j < array.length; ++j)
				System.out.println(array[i] + " ");
			}
		
	 
	static int partition(int[] arr, int left, int right) {
		int i = left;
		int j = right;
		int tmp;
		int pivot = arr.length-1;
		while (i <= j) {
			while (arr[i] < pivot)
				i++;
			while (arr[j] > pivot)
				j--;
			if (i <= j) {
				tmp = arr[i];
				arr[i] = arr[j];
				arr[j] = tmp;
				i++;
				j--;
			}
		}
		return i;
	} 
	static void quickSort(int[] arr, int left, int right) {
		int index = partition(arr, left, right);
		if (left < (index - 1)); {
			
		}
		quickSort(arr, left, index - 1);
		if (index < right) {
			quickSort(arr, index, right); 
		}
	}		
	//for (int j = 0; j < array.length; ++j)
	//	System.out.println(array[i] + " ");
}

                                              
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by: jb1devPosted on 2009-11-05 at 17:48:00ID: 25756046

That's because now you are past the original exception and are having a different problem.
I see you started another thread for it.

20120131-EE-VQP-002

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