Standard Template Library Programmer's Guide

inplace_merge , set_union , sort

Category: algorithms

Component type: function

Inplace_merge is an overloaded name: there are actually two inplace_merge functions.

template

inline void inplace_merge(BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last);

template

inline void inplace_merge(BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last, StrictWeakOrdering comp);

Inplace_merge combines two consecutive sorted ranges [first, middle) and [middle, last) into a single sorted range [first, last) . That is, it starts with a range [first, last) that consists of two pieces each of which is in ascending order, and rearranges it so that the entire range is in ascending order. Inplace_merge is stable, meaning both that the relative order of elements within each input range is preserved, and that for equivalent [1] elements in both input ranges the element from the first range precedes the element from the second.

The two versions of inplace_merge differ in how elements are compared. The first version uses operator< . That is, the input ranges and the output range satisfy the condition that for every pair of iterators i and j such that i precedes j , *j < *i is false . The second version uses the function object comp . That is, the input ranges and the output range satisfy the condition that for every pair of iterators i and j such that i precedes j , comp(*j, *i) is false .

Defined in algo.h.

For the first version:

• BidirectionalIterator is a model of Bidirectional Iterator.

• BidirectionalIterator is mutable.

• BidirectionalIterator 's value type is a model of LessThan Comparable.

• The ordering on objects of BidirectionalIterator 's value type is a strict weak ordering , as defined in the LessThan Comparable requirements.

• BidirectionalIterator is a model of Bidirectional Iterator.

• BidirectionalIterator is mutable.

• StrictWeakOrdering is a model of Strict Weak Ordering.

• BidirectionalIterator 's value type is convertible to StrictWeakOrdering 's argument type.

For the first version:

• [first, middle) is a valid range.

• [middle, last) is a valid range.

• [first, middle) is in ascending order. That is, for every pair of iterators i and j in [first, middle) such that i precedes j , *j < *i is false .

• [middle, last) is in ascending order. That is, for every pair of iterators i and j in [middle, last) such that i precedes j , *j < *i is false .

For the second version:

• [first, middle) is a valid range.

• [middle, last) is a valid range.

• [first, middle) is in ascending order. That is, for every pair of iterators i and j in [first, middle) such that i precedes j , comp(*j, *i) is false .

• [middle, last) is in ascending order. That is, for every pair of iterators i and j in [middle, last) such that i precedes j , comp(*j, *i) is false .

Inplace_merge is an adaptive algorithm: it attempts to allocate a temporary memory buffer, and its run-time complexity depends on how much memory is available. Inplace_merge performs no comparisons if [first, last) is an empty range. Otherwise, worst-case behavior (if no auxiliary memory is available) is O(N log(N)) , where N is last – first , and best case (if a large enough auxiliary memory buffer is available) is at most (last – first) – 1 comparisons.

int main() {

int A[] = { 1, 3, 5, 7, 2, 4, 6, 8 };

inplace_merge(A, A + 4, A + 8);

copy(A, A + 8, ostream_iterator(cout, " "));

// The output is "1 2 3 4 5 6 7 8".

}

[1] Note that you may use an ordering that is a strict weak ordering but not a total ordering; that is, there might be values x and y such that x < y , x > y , and x == y are all false. (See the LessThan Comparable requirements for a fuller discussion.) Two elements x and y are equivalent if neither x < y nor y < x . If you're using a total ordering, however (if you're using strcmp , for example, or if you're using ordinary arithmetic comparison on integers), then you can ignore this technical distinction: for a total ordering, equality and equivalence are the same.

merge , set_union , sort

Category: algorithms

Component type: function

Includes is an overloaded name; there are actually two includes functions.

template

bool includes(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2);

template

bool includes(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, StrictWeakOrdering comp);

Includes tests whether one sorted range includes another sorted range. That is, it returns true if and only if, for every element in [first2, last2) , an equivalent element [1] is also present in [first1, last1) [2]. Both [first1, last1) and [first2, last2) must be sorted in ascending order.

The two versions of includes differ in how they define whether one element is less than another. The first version compares objects using operator< , and the second compares objects using the function object comp .

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

For the first version:

• InputIterator1 is a model of Input Iterator.

• InputIterator2 is a model of Input Iterator.

• InputIterator1 and InputIterator2 have the same value type.