CODEWITHSUNDEEP
c++
John Doe
John Doe

Reputation: 1

My code for constructing n-odd magic squares isn't working

I'm trying to construct n-odd magic squares through the Siamese method

Here's my code 

#include <iostream>
#include <cstring>
using namespace std;

int main(){
    int N; cin >> N;
    int magicsquares[N][N];
    memset(magicsquares, 0, sizeof(magicsquares));

    int i = 0, j = N/2;
    int num = 1;
    while (num <= N*N){

        if (magicsquares[i][j] == 0){
            magicsquares[i][j] = num++;
            i = (i-1+N) % N;    
            j = (j+1) % N;
        } else{
            i = (i+2) % N;
            j = (j-1+N) % N;
            magicsquares[i][j] = num++;
        } 
    }

    for (int a = 0; a < N; a++){
        for (int b = 0; b < N; b++)
            cout << magicsquares[a][b] << " ";
        cout << endl;
    }
    return 0;
}

When I typed in 3, I expected it to come out like this:

8 1 6
3 5 7
4 9 2

But it came out like this:

0 9 0
3 0 8
7 0 2

What's wrong with my code? I can't figure it out

Upvotes: 0

Views: 50

Answers (1)

Emil M George
Emil M George

Reputation: 371

In the if branch (unfilled square), you fill a square and then set up i and j to point to the next square to be filled. When you encounter a filled square (else branch), you reverse the change in i and j and go down as per the algorithm, and fill it. But after that, you are not setting up i and j for the next move, like in the if branch. Setting i and j should be there for both branches. This should work:

    if (magicsquares[i][j] == 0){
        magicsquares[i][j] = num++;
    } else{
        i = (i+2) % N;
        j = (j-1+N) % N;
        magicsquares[i][j] = num++;
    } 
    i = (i-1+N) % N;    /* Setting up i and j for next fill */
    j = (j+1) % N;      /* This should be done in both cases */

Upvotes: 2

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