Java MergeSort using stacks

Question

I'm kind of new to this but trying to learn as quickly as possible. I am trying to implement a merge sort using stacks. I have no errors as such in my code but i get an array out of bounds error when i run the code. Any help would be greatly appreciated.

As i envision it, the merge sort function splits the stack in 2 (Left and Right) and then calls the merge function which sorts and merges them.

public static void main(String[] args) {
    Stack<Integer> myStack = new Stack<>();
    Random r = new Random();
    int size= 30;
    for (int i = 0; i < size;i++)
    {
        myStack.add(r.nextInt(200));
        System.out.println(myStack.peek());
    }
    MergeSort(myStack);
    System.out.println("-------");
    for (int i = 0; i < size; i++)
    {
        System.out.println(myStack.pop());
    }

}
private static Stack<Integer> MergeSort(Stack<Integer> input)
{
    Stack<Integer> Result;
    Stack<Integer> Left = new Stack<>();
    Stack<Integer> Right = new Stack<>();
    if (input.size() <= 1)
    {
        return input;
    }
    int midpoint = input.size() / 2;
    for (int i = 0; i < midpoint; i++)
    {
        Left.add(input.get(i));
    }
    for (int i = midpoint; i < input.size(); i++)
    {
        Right.add(input.get(i));
    }
    Left = MergeSort(Left);
    Right = MergeSort(Right);
    Result = Merge(Left, Right);

    return Result;
}

private static Stack<Integer> Merge(Stack<Integer> Left, Stack<Integer> Right)
{
    Stack<Integer> Result = new Stack<>();
    while (Left.size() > 0 && Right.size()>0)
    {
        if (Left.get(0) < Right.get(0))
        {
            Result.add(Left.get(0));
            Left.removeElementAt(0);
        }
        else
        {
            Result.add(Right.get(0));
            Right.removeElementAt(0);
        }
    }
    while (Left.size()> 0)
    {
     Result.add(Left.get(0));   
     Left.removeElementAt(0);
    }
    while (Right.size() > 0)
    {
      Result.add(Right.get(0));
      Right.removeElementAt(0);                    
    }
    return Result;
}

This is the console output.

run: 10 73 82 74 4 40 86 119 102 83 122 5 164 50 25 117 57 153 95 155 70 115 61 162 55 190 35 171 150

44

44 150 171 35 190 55 162 61 115 70 155 95 153 57 117 25 50 164 5 122 83 102 119 86 40 4 74 82 73 10 BUILD SUCCESSFUL (total time: 0 seconds)

Answer 1

In your function Merge: if (Left.get(0) < Right.get(0)) you wrote Result.get(Left.get(0)) instead of Result.add(Left.get(0))

Another thing: in your main function when printing the sorted stack: Do you really want to use .peek() (it only looks at the top of the stack)?