Algorithms (Matrix Stuff)

// Euklid
void euklid(int a, int b){
    int r = a % b;
    while (r > 0){
        a = b;
        b = r;
        r = a % b;
    }
    cout << b << endl;
}

// Triangle of *
void printTriangle(int n){
    for (int k = 1; k <= n; k++){
        for (j = 1; j <= n-k; j++){
            cout << " ";
        }
        for (i = 1; i <= 2*k-1; i++){
            cout << "*";
        }
        cout << endl;
    }
}

// Sum of diagonals of matrix
void printDiagonalSums(int mat[][m], int n){
    int principal = 0, secondary = 0;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            // Condition for principal diagonal
            if (i == j){
                principal += mat[i][j];
            }
            // Condition for secondary diagonal
            if ((i + j) == (n - 1)){
                secondary += mat[i][j];
            }
        }
    }
    cout << "Principal diagonal: " << principal << endl;
    cout << "Secondary diagonal: " << secondary << endl;
}

// Inversions count in array
int getInvCount(int &arr[], int n){
    int inv_count = 0;
    for (int i = 0; i < n - 1; i++){
        for (int j = i+1; j < n; j++){
            if (arr[i] > arr[j]){
                inv_count++;
            }
        }
    }
    return inv_count;
}

// Compute sum of 8 neighbours of element in 2D array
#define ROWS 8
#define COLS 8
int sum(int &matrix, int row, int col){
    int sum = 0;
    for (int i = -1; i < 2; i++){
        for (int j = -1; j < 2; j++){
            // skip center cell
            if (i == j){
                continue;
            }
            // skip rows out of range
            if ((i + row) < 0 || (i + row >= ROWS){
                continue;
            }
            // skip columns out of range
            if ((j + col) < 0 || (j + col >= COLS){
                continue;
            }
            // add to sum
            sum += matrix[i + row][j + col];
        }
    }
    return sum;
}

int make(int &result, int &source){
    for (int i = 0; i < ROWS; i++){
        for (int j = 0; j < COLS; j++){
            result[i][j] = sum(source, i, j);
        }
    }
}

int result[ROWS][COLS] = {0};
int source[ROWS][COLS] = {elements};
make(result, source);