I need to write a code to find an element in an integer array that is repeated exactly 'k' times but my code isn't working for a huge array

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This is the exact question from GeeksForGeeks.com

Quote:
Given an array of n integers. The task is to find the first element that occurs k number of times. If no element occurs k times the print -1. The distribution of integer elements could be in any range.

Note:

Quote:
The first line of input contains an integer T denoting the number of test cases. Then T test cases follow. The first line of each test case contains an integer N denoting the size of an array and the number K. The second line of each test case contains N space separated integers denoting elements of the array A[ ].

What I have tried:

This is my code. It doesn't give the proper output when the array size is 9383 and k = 6. It just returns 0 then. I would like your help in understanding where I may have gone wrong.

int FindRepeatedElement(vector<int>& nums, int k)
{
	sort(nums.begin(), nums.end());

	int count = 1, marked = 0;
	for (int i = 0; i < nums.size(); i++) // Here is a comparison
	{
		if (nums[i + 1] == nums[marked]) // Here is a comparison
		{
			count++;

			if (count == k) // Here is a comparison
				return nums[marked];
		}

		else
		{
			marked = i + 1;
			count = 1;
		}
	}
	return -1;
}

int main() {

	int t, n, k;
	
	
	cin >> t;

	while (t--)
	{
		cin >> n;
		cin >> k;
		vector<int> nums(n, 0);

		for (int i = 0; i < n; i++)
		{
			cin >> nums[i];
		}

		cout << FindRepeatedElement(nums, k) << endl;
	
	}

	system("pause");
	return 0;
}

Posted 2-Jun-17 17:00pm

Member 13192781

Updated 3-Jun-17 1:25am

v4

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Comments

[no name] 3-Jun-17 7:49am

Not a thing related to your problem, but anyway a problem in your code.
There is a chance of an "index out of range":

for (int i = 0; i < nums.size(); i++)
{
  if (nums[i + 1] == nums[marked])

2 solutions

Solution 1

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

private int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using teh debugger to find out why. Put a breakpoint on your line:

sort(nums.begin(), nums.end());

and run your app. Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?

This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Yes, I could probably tell you what "the problem" is - but it's not difficult to do this yourself, and you will learn something really worthwhile at the same time!

Posted 2-Jun-17 19:26pm

OriginalGriff

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Patrice T · Accepted Answer · 2017-06-03T01:25:00

Quote:
It doesn't give the proper output when the array size is 9383 and k = 6.

Without at least a reduced dataset, it is almost impossible to guess what go wrong in your code, even if we can see some suspicious things.

Quote:
It just returns 0

From your code, it means that the integer 0 is your answer. Did you check in the input if it is the correct answer ?

Algorithm problem in your code:
Suppose you have {7, 7, 1, 0, 1, 0} and k=2, what is the correct answer ? What is yours ?
As you can see, sorting the data have side effects.

As you have already been told, use the debugger to see what your code is doing.