How to save space and time with a mirrored NxN array
[ 0 3 9 2 ]
[ 3 0 5 6 ]
[ 9 5 0 1 ]
[ 2 6 1 0 ]

#include <QVector>
#include <QDebug>
#include <QString>

class MirroredArray
{
public:
    MirroredArray(int sideLength)
    {
        values.fill(0, sideLength*(sideLength+1)/2);
        this->s = sideLength;
    }

    int get(int r, int c)
    {
        if(c > r)
        {
          return values.at(s*r-(r-1)*r/2 + c-r);
        }
        else
        {
          return values.at(s*c-(c-1)*c/2 + r-c);
        }
    }

    void set(int r, int c, int value)
    {
        if(c > r)
        {
          values[s*r-(r-1)*r/2 + c-r] = value;
        }
        else
        {
          values[s*c-(c-1)*c/2 + r-c] = value;
        }
    }
    int getSide()
    {
        return s;
    }

    QString contentsToString()
    {
        QString temp = "(" + QString::number(values.size()) + ") - ";
        for(int i = 0; i<values.size(); i++)
          temp += QString::number(i) + ", ";
        return temp;
    }

private:
    QVector <int> values;
    int s;
};

01234  (n=5)
 5678
  901
   23
    4