I need help with a two-dimensional table

blaster123 (24)
Its given the matrix T[n][n] with integer elements. It is considered that the two diagonals i divide the matrix into four areas: north, south, east, west (the elements on the diagonals are not part of no area). Compose a program that will count the elements located in the northern area. Can you make this tabel just with iostream please :*
jonnin (11437)
you don't need the table, all you need is n.
the first part of the sum is
* 1 2 3 4 ... * (n-2)
the next row is
** 1 2 3 4 ... ** (n-4)
so is there a pattern that just gives you the answer using only N?
There may be 2 patterns, one for even N, one for odd N, but regardless, I believe you can do it without the table if you play with it a little.
Last edited on
seeplus (6592)
The sums are:

n = 3; 1
n = 4; 2
n = 5; 3 + 1
n = 6; 4 + 2
n = 7; 5 + 3 + 1

So:

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#include <iostream>

int main()
{
	int n {}, cnt {};

	std::cout << "Enter n: ";
	std::cin >> n;

	for (int i = n - 2; i > 0; i -= 2)
		cnt += i;

	std::cout << "Number of elements are: " << cnt << '\n';
}

seeplus (6592)
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#include <iostream>

int main()
{
	const size_t max_size {20};

	for (size_t n = 1; n <= max_size; ++n) {
		size_t cnt {};

		for (int i = n - 2; i > 0; i -= 2)
			cnt += i;

		std::cout << n << "  " << cnt << '\n';
	}
}



1  0
2  0
3  1
4  2
5  4
6  6
7  9
8  12
9  16
10  20
11  25
12  30
13  36
14  42
15  49
16  56
17  64
18  72
19  81
20  90

lastchance (6980)
terms1 wrote:
count the elements located in the northern area

Are you sure that you just want to count them?

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#include <iostream>
using namespace std;

int main()
{
   int n;
   cout << "Input n: ";   cin >> n;
   cout << "Number of northern elements = " << ( n * ( n - 2 ) + ( n % 2 ) ) / 4 << '\n';
}


Input n: 13
Number of northern elements = 36
Last edited on
blaster123 (24)
yes
blaster123 (24)
is this the right program?
seeplus (6592)
You tell us. Does it produce the expected values?

NB as the matrix is square, the numbers in each of the 4 areas are the same.
blaster123 (24)
yes its right, thanks guys
blaster123 (24)
@seeplus can you explain how you did the first program?
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