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Thread: MergeSort not working Helppp please :(

  1. #1
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    Default MergeSort not working Helppp please :(

    I've been working on this mergeSort that has to read from a file then give me the size and then print out the sorted array. However it's giving me the size and printing out the list without sorting it... Helppp please

    Here's my code:
    import java.io.File;
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.util.InputMismatchException;
    import java.util.NoSuchElementException;
    import java.util.Scanner;
     
    /**
     *
     * @author fluffy
     */
    public class Numbers {
     
        int[] data;
        int size;
     
        Numbers(String fileName) throws IOException {
            data = openFile(fileName);
            data = mergeSort(data);
     
            for (int i = 0; i < data.length; i = i + 1) {
                System.out.println("*" + data[i]);
            }
        }
     
        public int[] openFile(String fileName) throws
                IOException, ArrayIndexOutOfBoundsException,
                InputMismatchException, NoSuchElementException {
     
            int[] a = new int[10];
            int i = 0;
            int k = 0;
            try {
                File inFile = new File(fileName);
                Scanner in = new Scanner(inFile);
     
                //while(in.hasNext()){
                do {
     
                    try {
                        k = in.nextInt();
     
                        try {
     
                            a[i] = k;
                        } catch (ArrayIndexOutOfBoundsException e) {
                            System.out.println("Array bound error");
                            a = grow(a);
                            a[i] = k;
                        }
                        i = i + 1;
                    } catch (InputMismatchException e) {
                        in.next();
                    }
                } while (true);
     
     
            } catch (IOException e) {
                //System.out.println("File 2 not found in openFile3  " + e.getMessage());
            } catch (NoSuchElementException e) {
                size = i - 1;
            }
     
            System.out.println("Size of the array " + size);
     
            return a;
        }
     
        private static int[] grow(int[] a) {
            int[] b = new int[(a.length) * 2];
            for (int i = 0; i <
                    a.length; i =
                            i + 1) {
                b[i] = a[i];
            }
     
            return b;
     
        }
     
        public static int[] mergeSort(int[] data) {
            if (data.length > 1) {
     
                int mid = data.length / 2;
     
                int[] first = new int[mid];
                int[] second = new int[data.length - mid];
     
                for (int i = 0; i < first.length; i = i + 1) {
                    first[i] = data[i];
                }
                for (int i = 0; i < second.length; i = i + 1) {
                    second[i] = data[i + mid];
                }
     
                first = mergeSort(first);
                second = mergeSort(second);
                data = merge(first, second);
     
            }
     
            return data;
        }
     
     
        public static int[] merge(int[] first, int[] second) {
            int i = 0, j = 0;
            int k = 0;
            int[] mergeData = new int[first.length + second.length];
     
            if (i < first.length && j < second.length) {
                if (first[i] < second[j]) {
                    mergeData[k] = first[i];
                    i = i + 1;
                    k = k + 1;
                } else {
                    mergeData[k] = second[j];
                    j = j + 1;
                    k = k + 1;
                }
     
                for (; i < first.length; i = i + 1) {
                    mergeData[k] = first[i];
                    k = k + 1;
                }
                for (; j < second.length; j = j + 1) {
                    mergeData[k] = second[j];
                    k = k + 1;
                }
     
     
            }
            return mergeData;
        }
    }
    Last edited by helloworld922; May 16th, 2010 at 08:21 PM. Reason: please use [code] tags


  2. #2
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    Default Re: MergeSort not working Helppp please :(

    Your MergeSort method never returns the sorted list.

        public static int[] mergeSort(int[] data) {
            if (data.length > 1) {
     
                int mid = data.length / 2;
     
                int[] first = new int[mid];
                int[] second = new int[data.length - mid];
     
                for (int i = 0; i < first.length; i = i + 1) {
                    first[i] = data[i];
                }
                for (int i = 0; i < second.length; i = i + 1) {
                    second[i] = data[i + mid];
                }
     
                first = mergeSort(first);
                second = mergeSort(second);
                data = merge(first, second);
                [b]return data;[/b] // need this line
            }

  3. #3
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    Default Re: MergeSort not working Helppp please :(

    it does have the return data; after that } because if i put it where u placed it at the beggining its going to tell me im missing the return statement... i tried it =/

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    Default Re: MergeSort not working Helppp please :(

    The sorting code is buggy - it does partially sort the list, but not fully.

    I suggest you pick a trivial set of values and step through each method by hand keeping track of what happens on paper.

  5. #5
    Super Moderator helloworld922's Avatar
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    Default Re: MergeSort not working Helppp please :(

    Ahh, didn't look through it that closely ::blush::
    dlorde's right, there is a flaw in your merge method. Do what he says and see if you can figure out what it is

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