sort one array and other array following?

Question

here is the C++ sample

int a[1000] = {3,1,5,4}
int b[1000] = {7,9,11,3}

how do i make it so if i sort array a, array b also following array a

Answer 1

The simplest way is to rearrange your data into an array-of-structs instead of a pair of arrays so that each datum is contiguous; then, you can use an appropriate comparator. For example:

struct CompareFirst
{
    bool operator() (const std::pair& lhs, const std::pair& rhs)
    {
        return lhs.first < rhs.first;
    }
};

// c[i].first contains a[i], c[i].second contains b[i] for all i
std::pair c[1000];
std::sort(c, c+1000, CompareFirst());

If you can't refactor your data like that, then you need to define a custom class that acts as a RandomAccessIterator:

struct ParallalArraySortHelper
{
    ParallelArraySortHelper(int *first, int *second)
        : a(first), b(second)
    {
    }

    int& operator[] (int index) { return a[index]; }
    int operator[] const (int index) { return a[index]; }

    ParallelArraySortHelper operator += (int distance)
    {
        a += distance;
        b += distance;
        return *this;
    }
    // etc.
    // Rest of the RandomAccessIterator requirements left as an exercise

    int *a;
    int *b;
};
...
int a[1000] = {...};
int b[1000] = {...};
std::sort(ParallalArraySortHelper(a, b), ParallelArraySortHelper(a+1000, b+1000));