# Re: Sorting two arrays with one call to sort()?

From:
Ben Rudiak-Gould <br276deleteme@cam.ac.uk>
Newsgroups:
comp.lang.c++.moderated,comp.lang.c++
Date:
Sat, 22 Sep 2007 13:12:42 CST
Message-ID:
<fd3ip2\$bj2\$1@gemini.csx.cam.ac.uk>
John wrote:

I have two separate arrays A and B. The comparison function only
depends on elements in A (keys are in A),
but the swap() function needs to swap not only A[i],A[j], but also
B[i],B[j] ; whenever it swaps A[i],A[j].
Can this be done using internal sort() of C++?

I should hope so, since the main point of the STL is to decouple algorithms
from data structures. Something like this ought to work:

struct double_iterator {

T* const a; U* const b; size_t i;

struct ref {
T& p; U& q;
ref(T& p, U& q) : p(p), q(q) {}
};

ref operator*() { return ref(a[i], b[i]); }

// ...

};

inline void operator=(ref x, ref y) { x.p = y.p; x.q = y.q; }
inline bool operator<(ref x, ref y) { return x.p < y.p; }

// ...

std::sort(double_iterator(A,B,0), double_iterator(A,B,size));

I think this will be as efficient as a hand-coded sort if you have a decent
compiler.

-- Ben

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