调用 mergeSort 方法时出现 Stack_Overflow_error

Question

I've been doing this problem:

I created one file which takes random numbers and I stored those numbers in a SinglyLinkedList data structure and I'd like to perform a mergeSort to sort these random numbers.

Everything works fine for smaller no of input. But when I insert 10000 numbers, it starts giving 'stack_overflow' error at around 9800 no(at displaying numbers only) and when I insert 0.1 million numbers- it works well till 99700 numbers but then it starts showing errors for the rest of the numbers.

So what exactly the reason would be behind this error (I know it's because it gets lost in recursive function) Please help me out here, I'm not able to track the problem which causes this error.

Here's my main method code:

FileReader fr = new FileReader("C://my_folder//file_List.txt");
    BufferedReader br = new BufferedReader(fr);

    LinkedListNode lln = new LinkedListNode();

    String str;

    while((str=br.readLine())!=null){

        /* This insertAtEnd appends the number to the SinglyLinkedList*/
        lln.insertAtEnd(Integer.parseInt(str));
        System.out.println(" "+str);
    }
     /*This method displays the elements of a LinkedList*/
    Node res = lln.traverse();
    System.out.println("\n");
    mergeSortLinkedList ms = new mergeSortLinkedList();
    ms.sort(res);

here's my sort method code:

public void sort(Node n){
    Node tmp = n;

    MergeSort(tmp);
}

Node a;
Node b;

public void MergeSort(Node headRef){


    Node head1 = headRef;

    if(head1 == null || head1.next == null){
        return;
    } 
    System.out.print("hi..");
    Node Euler = splitList(head1);
    printList(Euler);

}

/* perform merge sort on the linked list */

public Node splitList(Node head1){

    Node slow;
    Node fast;
    Node left, right;


    if(head1 == null || head1.next == null){
        left  = head1;
        right = null;

        return head1;
    }
    else{

        slow = head1;
        fast = head1.next;


        while(fast!=null){

            fast = fast.next;

            if(fast!=null){

                slow = slow.next;
                fast = fast.next;
            }
        }

        left = head1;
        right = slow.next;

        slow.next = null;


    }



    return SortedMerge(splitList(left),splitList(right));
}

/* merge the lists.. */
public Node SortedMerge(Node a, Node b){

    Node result = null;

    if(a == null){
        return b;
    }
    else if( b == null){
        return a;
    }

    if(a.data < b.data){
        result = a;
        result.next = SortedMerge(a.next, b);//getting error at this line
    }
    else{
        result = b;
        result.next = SortedMerge(a,b.next);//getting error at this line
    }

    return result;
}


public void printList(Node Euler){
    System.out.println("\nPrinting sorted elements");
    Node Ref = Euler;
    int count = 0;

     while(Ref!=null){
        count++;
        System.out.println(count+"-"+Ref.data);
        Ref = Ref.next;
    }
}

Answer 1

have you considered using Collections.sort() from the JDK, which will do a merge-sort? Java 8 has also a parallelSort which does a parallel merge-sort.

Answer 2

I'd like to give you a update.

By changing the stack size, I did able to run my program properly. The reason it was causing Exception in thread "main" java.lang.StackOverflowError is because it was getting out of stack size.

So I searched around and got this solution.

Go to the project properties- Inside run, go to the VM option and put this in argument -Xss100m to make it run! Now it is able to sort more than 1 million numbers :D

Other suggestions / solutions are welcome.