compute the two smallest numbers

[yokaygirl143]

i am writing a simple java program but everything i do it seems to not work. i need to find the smallest and second smallest number in a set. please help me understand what i have done wrong.

heres what i figured(but doesn't work fully):

public class TwoSmallest
{
    public static void main(String[] args)
    {
    int size = IO.readInt();
    if (size <= 0)
        {
        IO.reportBadInput();
        return;
        }
    int counter = 1;
    double number = IO.readDouble();
    double smallest  = 100;
    double smaller = 0;
    do
        {
        if (number < smallest)
            {
            smallest = number;
            counter = counter++;
            }
        else if (number > smallest && smallest < smaller)
            {
            smaller = number;
            counter = counter++;
            }
        else
            {
            counter = counter++;
            continue;
            }
        }
    while (counter <= size);
    IO.outputDoubleAnswer(smallest);
    IO.outputDoubleAnswer(smaller);
    return;
    }
}

[Ganon11]

First of all, setting 100 to smallest is a messy way of doing this program. (Additionally, it won't work - consider if the user enters 101, 102, 103...200. Then your program thinks 0 is the smallest, and 100 is the second smallest, both of which were never actually entered by the user.) Consider the basic case, when the user enters only two numbers. Then the smallest number is, well, the smaller of these two, and the second smallest is the larger. If you take care of this simple case before moving onto the 3rd, 4th, 5th... number the user enters, your program will be much better.

Next, why are you using a do...while loop? You know exactly how many times the loop should execute, so use a for...loop.

Now, consider some point in the middle of your loop. Your user has entered some number of values (say 5). At this point, smallest = 2, and smaller = 5. Now, the user enters 0. 0 < smallest, so smallest should now = 0. Your code does this. But what is smaller? smaller is certainly not 5, it should be 1, right? Your logic does not account for this.

So now we have smallest = 0, and smaller = 2. Now the user enters 1. 1 > smallest, so we don't have to change that. But 1 < smaller, so we have to change that value - smaller should now be 1.

So now smallest = 0, and smaller = 1. Suppose the user enters 10. Well, 10 > smallest, and 10 > smaller, so you don't have to do anything.

Now you have the general behavior for any possible case - you should be able to code this pretty easily.

[JosAH]

[quote=yokaygirl143]i am writing a simple java program but everything i do it seems to not work. i need to find the smallest and second smallest number in a set. please help me understand what i have done wrong.

Why not copy your entire set to a TreeSet and take the first two elements?

kind regards,

Jos

[Ganon11]

[quote=JosAH]

i am writing a simple java program but everything i do it seems to not work. i need to find the smallest and second smallest number in a set. please help me understand what i have done wrong.

Why not copy your entire set to a TreeSet and take the first two elements?

kind regards,

Jos

Because it would be less efficient?

Inserting all elements: O(n log n)
Getting the first two: At best, O(log n), at worst, O(n)

Doing it this way: O(n)

[JosAH]

[quote=Ganon11]

Because it would be less efficient?

Inserting all elements: O(n log n)
Getting the first two: At best, O(log n), at worst, O(n)

Doing it this way: O(n)

I know, I know; but the OP doesn't have the slightest idea how to solve this now.
An inefficient solution might start a little idea (as in 'the next step').

kind regards,

Jos

[Ganon11]

[quote=JosAH]

I know, I know; but the OP doesn't have the slightest idea how to solve this now.
An inefficient solution might start a little idea (as in 'the next step').

kind regards,

Jos

True, functionality is more important than efficiency, but since I'm in a class that focuses on efficiency, it's the first response that came to mind. Have to stay on top of these things when I have an exam on Thursday.

[JosAH]

[quote=Ganon11]

True, functionality is more important than efficiency, but since I'm in a class that focuses on efficiency, it's the first response that came to mind. Have to stay on top of these things when I have an exam on Thursday.

My entire professional/mathematical life revolves around big-oh's ;-) Best of luck
with your exams.

kind regards,

Jos