Difference between revisions of "cpp/algorithm/partition point"
(Changed complexity to use math) |
(number of iterator increments is O(N) --- copy wording from std::lower_bound, and wikilink it) |
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===Complexity=== | ===Complexity=== | ||
| − | + | Given {{c|1=N = std::distance(first, last)}}, performs {{math|O(log N)}} applications of the predicate {{tt|p}}. | |
| + | However, for non-{{lc|RandomAccessIterator}}s, the number of iterator increments is {{math|O(N)}}. | ||
===Example=== | ===Example=== | ||
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{{dsc begin}} | {{dsc begin}} | ||
{{dsc inc | cpp/algorithm/dsc is_sorted}} | {{dsc inc | cpp/algorithm/dsc is_sorted}} | ||
| + | {{dsc inc | cpp/algorithm/dsc lower_bound}} | ||
{{dsc end}} | {{dsc end}} | ||
Revision as of 19:38, 23 April 2017
| Defined in header <algorithm>
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||
| template< class ForwardIt, class UnaryPredicate > ForwardIt partition_point( ForwardIt first, ForwardIt last, UnaryPredicate p ); |
(1) | (since C++11) |
Examines the partitioned (as if by std::partition) range [first, last) and locates the end of the first partition, that is, the first element that does not satisfy p or last if all elements satisfy p.
Contents |
Parameters
| first, last | - | the partitioned range of elements to examine |
| p | - | unary predicate which returns true for the elements found in the beginning of the range. The expression p(v) must be convertible to bool for every argument |
| Type requirements | ||
Return value
The iterator past the end of the first partition within [first, last) or last if all elements satisfy p.
Complexity
Given N = std::distance(first, last), performs O(log N) applications of the predicate p.
However, for non-RandomAccessIterators, the number of iterator increments is O(N).
Example
#include <algorithm> #include <array> #include <iostream> #include <iterator> int main() { std::array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; auto is_even = [](int i){ return i % 2 == 0; }; std::partition(v.begin(), v.end(), is_even); auto p = std::partition_point(v.begin(), v.end(), is_even); std::cout << "Before partition:\n "; std::copy(v.begin(), p, std::ostream_iterator<int>(std::cout, " ")); std::cout << "\nAfter partition:\n "; std::copy(p, v.end(), std::ostream_iterator<int>(std::cout, " ")); }
Output:
Before partition:
8 2 6 4
After partition:
5 3 7 1 9See also
| (C++11) |
checks whether a range is sorted into ascending order (function template) |
| returns an iterator to the first element not less than the given value (function template) |
