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
- template<typename ForwardIterator, typename Type, typename Compare> bool std::binary_search (ForwardIterator first, ForwardIterator last, const Type &__val, Compare comp)
- template<typename ForwardIterator, typename Type> bool std::binary_search (ForwardIterator first, ForwardIterator last, const Type &__val)
- template<typename ForwardIterator, typename Type, typename Compare> pair< ForwardIterator, ForwardIterator > std::equal_range (ForwardIterator first, ForwardIterator last, const Type &__val, Compare comp)
- template<typename ForwardIterator, typename Type> pair< ForwardIterator, ForwardIterator > std::equal_range (ForwardIterator first, ForwardIterator last, const Type &__val)
- template<typename ForwardIterator, typename Type, typename Compare> ForwardIterator std::lower_bound (ForwardIterator first, ForwardIterator last, const Type &__val, Compare comp)
- template<typename ForwardIterator, typename Type> ForwardIterator std::lower_bound (ForwardIterator first, ForwardIterator last, const Type &__val)
- template<typename ForwardIterator, typename Type, typename Compare> ForwardIterator std::upper_bound (ForwardIterator first, ForwardIterator last, const Type &__val, Compare comp)
- template<typename ForwardIterator, typename Type> ForwardIterator std::upper_bound (ForwardIterator first, ForwardIterator last, const Type &__val)
Function Documentation
bool binary_search |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 3941 of file stl_algo.h.
References std::lower_bound(). |
bool binary_search |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 3909 of file stl_algo.h.
References std::lower_bound(). |
pair<ForwardIterator, ForwardIterator> equal_range |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 but does not actually call those functions. Definition at line 3851 of file stl_algo.h.
References std::advance(), std::distance(), std::lower_bound(), and std::upper_bound(). |
pair<ForwardIterator, ForwardIterator> equal_range |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 but does not actually call those functions. Definition at line 3789 of file stl_algo.h.
References std::advance(), std::distance(), std::lower_bound(), and std::upper_bound(). |
ForwardIterator lower_bound |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 2665 of file stl_algo.h.
References std::advance(), and std::distance().
Referenced by map< Key, Type, Compare, Allocator >::operator[](). |
ForwardIterator lower_bound |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 2610 of file stl_algo.h.
References std::advance(), and std::distance().
Referenced by std::binary_search(), and std::equal_range(). |
ForwardIterator upper_bound |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 2764 of file stl_algo.h.
References std::advance(), and std::distance(). |
ForwardIterator upper_bound |
( |
ForwardIterator |
first, |
|
|
ForwardIterator |
last, |
|
|
const Type & |
__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 2712 of file stl_algo.h.
References std::advance(), and std::distance().
Referenced by std::equal_range(). |
Generated on Sun Sep 12 15:50:08 2004 for libstdc++ source by
1.3.8