Return the first perfect square that is greater than its integer argument

Question

I need to write a function that returns the first perfect square that is greater than its integer argument. A perfect square is an integer that is equal to some integer squared. For example 16 is a perfect square because 16 = 4 * 4. However 15 is not a perfect square because there is no integer n such that 15 = n*n.

public static int NextPerfectSquare(int inputNumber)
{
    if (inputNumber < 0) return 0;
    inputNumber++;
    var result = Math.Sqrt(inputNumber);
    var resultnumber = (int) result;
    if (resultnumber == result) return inputNumber;
    resultnumber++;
    return resultnumber * resultnumber;

}

Is this right?

Could you clarify the meaning of a line "if (resultnumber == result)..."? You are comparing double and int. — , May 14 '11 at 18:43
yeah i am too confused i think there is no need of these line if (resultnumber == result) return inputNumber;??? and returning inputNumber violates returning perfect square??? — LC 웃, Aug 01 '15 at 14:49

score 3 · Accepted Answer · answered May 14 '11 at 17:21

The basic solution looks good. You may want to consider:

Should comments be added to this function? Maybe not for an exam, but worth considering.
Use consistent casing for your parameters/local variables. Consider whether they could be named more clearly.
What about boundary conditions? You've got the negative case covered, but what if inputNumber is close to int.MaxValue so that the next perfect square would be > MaxValue?

score 1 · Answer 2 · answered May 14 '11 at 17:20

1

Looks right to me. Handles negative numbers, handles some arbitrary value which is not a perfect square properly, handles perfect squares properly, so I'll go with yes.

answered May 14 '11 at 17:20

zellio

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score 1 · Answer 3 · answered May 14 '11 at 17:22

Kind of.

But I'm loathe to leave it at that because you could have verified this yourself quite easily by running some tests.

System.Console.WriteLine("-10 => {0}", NextPerfectSquare(-10));
System.Console.WriteLine("0 => {0}", NextPerfectSquare(0));
System.Console.WriteLine("1 => {0}", NextPerfectSquare(1));
System.Console.WriteLine("15 => {0}", NextPerfectSquare(15));
System.Console.WriteLine("21 => {0}", NextPerfectSquare(21));
System.Console.WriteLine("24 => {0}", NextPerfectSquare(24));
System.Console.WriteLine("36 => {0}", NextPerfectSquare(36));
System.Console.WriteLine("Max => {0}", NextPerfectSquare(int.MaxValue));
System.Console.WriteLine("Min => {0}", NextPerfectSquare(int.MinValue));

-10 => 0
0 => 1
1 => 4
15 => 16
21 => 25
24 => 25
36 => 49
Max => 1
Min => 0

So you could probably optimize it a little for bonus points?

Make it safe for large numbers. i.e. long/Int64

Make it safe from max value overflows. (try entering int.MaxValue as your input)

score 1 · Answer 4 · answered May 14 '11 at 17:50

Seems to be working correct.

I would personally go for something like:

public static int Next(int inputNumber)
{
    if (inputNumber < 0) return 0;

    int perfectWidth = (int)Math.Floor(Math.Sqrt(inputNumber));
    return (int)Math.Pow(perfectWidth + 1, 2);
}

as i think it shows the logic a bit clearer. But that might be my personal preferences of course ;)

score 0 · Answer 5 · answered Aug 01 '15 at 14:55

You can reduce your code as

public static int NextPerfectSquare(int inputNumber)
{
    if (inputNumber < 0) return 0;
    var result = Math.Sqrt(inputNumber);
    var resultnumber = (int) result;
    resultnumber++;
    return resultnumber * resultnumber;

}

Return the first perfect square that is greater than its integer argument

5 Answers5