Binary search algorithms


Detailed Description

These algorithms are variations of a classic binary search. They all assume that the sequence being searched is already sorted.

The number of comparisons will be logarithmic (and as few as possible). The number of steps through the sequence will be logarithmic for random-access iterators (e.g., pointers), and linear otherwise.

The LWG has passed Defect Report 270, which notes: The proposed resolution reinterprets binary search. Instead of thinking about searching for a value in a sorted range, we view that as an important special case of a more general algorithm: searching for the partition point in a partitioned range. We also add a guarantee that the old wording did not: we ensure that the upper bound is no earlier than the lower bound, that the pair returned by equal_range is a valid range, and that the first part of that pair is the lower bound.

The actual effect of the first sentence is that a comparison functor passed by the user doesn't necessarily need to induce a strict weak ordering relation. Rather, it partitions the range.

Functions


Function Documentation

bool std::binary_search _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val,
_Compare  __comp
 

Determines whether an element exists in a range.

Parameters:
first An iterator.
last Another iterator.
val The search term.
comp A functor to use for comparisons.
Returns:
True if val (or its equivelent) is in [first,last ].
Note that this does not actually return an iterator to val. For that, use std::find or a container's specialized find member functions.

The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 3954 of file stl_algo.h.

References __glibcxx_function_requires, and std::lower_bound().

bool std::binary_search _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val
 

Determines whether an element exists in a range.

Parameters:
first An iterator.
last Another iterator.
val The search term.
Returns:
True if val (or its equivelent) is in [first,last ].
Note that this does not actually return an iterator to val. For that, use std::find or a container's specialized find member functions.

Definition at line 3922 of file stl_algo.h.

References __glibcxx_function_requires, and std::lower_bound().

pair<_ForwardIterator, _ForwardIterator> std::equal_range _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val,
_Compare  __comp
 

Finds the largest subrange in which val could be inserted at any place in it without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
comp A functor to use for comparisons.
Returns:
An pair of iterators defining the subrange.
This is equivalent to
    std::make_pair(lower_bound(first, last, val, comp),
                   upper_bound(first, last, val, comp))
but does not actually call those functions.

Definition at line 3864 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), std::distance(), std::lower_bound(), and std::upper_bound().

pair<_ForwardIterator, _ForwardIterator> std::equal_range _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val
 

Finds the largest subrange in which val could be inserted at any place in it without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
Returns:
An pair of iterators defining the subrange.
This is equivalent to
    std::make_pair(lower_bound(first, last, val),
                   upper_bound(first, last, val))
but does not actually call those functions.

Definition at line 3802 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), std::distance(), std::lower_bound(), and std::upper_bound().

_ForwardIterator std::lower_bound _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val,
_Compare  __comp
 

Finds the first position in which val could be inserted without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
comp A functor to use for comparisons.
Returns:
An iterator pointing to the first element "not less than" val, or end() if every element is less than val.
The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 2678 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), and std::distance().

_ForwardIterator std::lower_bound _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val
 

Finds the first position in which val could be inserted without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
Returns:
An iterator pointing to the first element "not less than" val, or end() if every element is less than val.

Definition at line 2623 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), and std::distance().

Referenced by std::__merge_adaptive(), std::__merge_without_buffer(), __gnu_cxx::__stl_next_prime(), std::binary_search(), prime_rehash_policy::bkt_for_elements(), std::equal_range(), prime_rehash_policy::need_rehash(), prime_rehash_policy::next_bkt(), and map::operator[]().

_ForwardIterator std::upper_bound _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val,
_Compare  __comp
 

Finds the last position in which val could be inserted without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
comp A functor to use for comparisons.
Returns:
An iterator pointing to the first element greater than val, or end() if no elements are greater than val.
The comparison function should have the same effects on ordering as the function used for the initial sort.

Definition at line 2777 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), and std::distance().

_ForwardIterator std::upper_bound _ForwardIterator  __first,
_ForwardIterator  __last,
const _Tp &  __val
 

Finds the last position in which val could be inserted without changing the ordering.

Parameters:
first An iterator.
last Another iterator.
val The search term.
Returns:
An iterator pointing to the first element greater than val, or end() if no elements are greater than val.

Definition at line 2725 of file stl_algo.h.

References __glibcxx_function_requires, std::advance(), and std::distance().

Referenced by std::__merge_adaptive(), std::__merge_without_buffer(), and std::equal_range().


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