In this section we describe the generic algorithms in the C++ Standard Library that are specific to ordered collections. These algorithms are summarized in Table 20:
Algorithm | Purpose |
Sorting algorithms | |
partial_sort() | Sorts only part of sequence |
partial_sort_copy() | Partial sorts into copy |
sort() | Rearranges sequence, places in order |
stable_sort() | Sorts, retaining original order of equal elements |
Nth largest element algorithm | |
nth_element() | Locates nth largest element |
Binary search algorithms | |
binary_search() | Searches, returning a boolean value |
equal_range() | Searches, returning both positions |
lower_bound() | Searches, returning first position |
upper_bound() | Searches, returning last position |
Merge ordered sequences algorithm | |
merge() | Combines two ordered sequences |
Set operations algoithms | |
includes() | Compares two sorted sequences and returns true if every element in the range [first2, last2) is contained in the range [first1, last1) |
set_intersection() | Forms intersection of two sets |
set_difference() | Forms difference of two sets |
set_symmetric_difference() | Forms symmetric difference of two sets |
set_union() | Forms union of two sets |
Heap operations algorithms | |
make_heap() | Turns a sequence into a heap |
push_heap() | Adds a new value to the heap |
pop_heap() | Removes largest value from the heap |
sort_heap() | Turns heap into sorted collection |
Ordered collections can be created using the C++ Standard Library in a variety of ways. For example:
The containers set, multiset, map, and multimap are ordered collections by definition.
A list can be ordered by invoking the std::sort() member function.
A vector, deque, or ordinary C++ array can be ordered by using one of the sorting algorithms described in Section 14.2.
Like the generic algorithms described in Section 13, the algorithms described here are not specific to any particular container class. This means that they can be used with a wide variety of types. However, many of them do require the use of random-access iterators. For this reason they are most easily used with vectors, deques, or ordinary arrays.
Almost all the algorithms described in this section have two versions. The first version uses operator<() for comparisons appropriate to the container element type. The second, and more general, version uses an explicit comparison function object, which we will write as Compare. This function object must be a binary predicate (see Section 3.3). Since this argument is optional, we will write it within square brackets in the description of the argument types.
A sequence is considered ordered if for every valid or denotable iterator i with a denotable successor j, the comparison Compare(*j, *i) is false. Note that this does not necessarily imply that Compare(*i, *j) is true. It is assumed that the relation imposed by Compare is transitive, and induces a total ordering on the values.
In the descriptions that follow, two values x and y are said to be equivalent if both Compare(x, y) and Compare(y, x) are false. Note that this need not imply that x == y.
As with the algorithms described in Chapter 13, before you can use any of these algorithms in a program you must include the algorithm header file:
#include <algorithm>