```// Copyright (C) 2011  Davis E. King (davis@dlib.net)
#undef DLIB_DISJOINT_SUBsETS_ABSTRACT_Hh_
#ifdef DLIB_DISJOINT_SUBsETS_ABSTRACT_Hh_

#include <vector>
#include "../algs.h"

namespace dlib
{

// ----------------------------------------------------------------------------------------

class disjoint_subsets
{
/*!
INITIAL VALUE
- size() == 0

WHAT THIS OBJECT REPRESENTS
This object represents a set of integers which is partitioned into
a number of disjoint subsets.  It supports the two fundamental operations
of finding which subset a particular integer belongs to as well as
merging subsets.
!*/
public:

void clear (
) noexcept;
/*!
ensures
- #size() == 0
- returns this object to its initial value
!*/

void set_size (
unsigned long new_size
);
/*!
ensures
- #size() == new_size
- for all valid i:
- #find_set(i) == i
(i.e. this object contains new_size subsets, each containing exactly one element)
!*/

size_t size (
) const noexcept;
/*!
ensures
- returns the total number of integer elements represented
by this object.
!*/

unsigned long find_set (
unsigned long item
) const;
/*!
requires
- item < size()
ensures
- Each disjoint subset can be represented by any of its elements (since
the sets are all disjoint).  In particular, for each subset we define
a special "representative element" which is used to represent it.
Therefore, this function returns the representative element for the
set which contains item.
- find_set(find_set(item)) == find_set(item)
- Note that if A and B are both elements of the same subset then we always
have find_set(A) == find_set(B).
!*/

unsigned long merge_sets (
unsigned long a,
unsigned long b
);
/*!
requires
- a != b
- a < size()
- b < size()
- find_set(a) == a
(i.e. a is the representative element of some set)
- find_set(b) == b
(i.e. b is the representative element of some set)
ensures
- #find_set(a) == #find_set(b)
(i.e. merges the set's containing a and b)
- returns #find_set(a)
!*/
};

// ----------------------------------------------------------------------------------------

}

#endif // DLIB_DISJOINT_SUBsETS_ABSTRACT_Hh_

```