Difference between revisions of "cpp/algorithm/minmax element"
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Revision as of 18:14, 2 November 2012
Template:ddcl list begin <tr class="t-dsc-header">
<td><algorithm>
<td></td> <td></td> </tr> <tr class="t-dcl ">
<td >std::pair<ForwardIt,ForwardIt>
<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">
<td >std::pair<ForwardIt,ForwardIt>
<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end
Finds the greatest and the smallest element in the range [first, last). The first version uses operator< to compare the values, the second version uses the given comparison function comp.
Contents |
Parameters
| first, last | - | forward iterators defining the range to examine |
| cmp | - | comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if if *a is less than *b.The signature of the comparison function should be equivalent to the following: bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) |
| Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator.
| ||
Return value
a pair consisting of an iterator to the smallest element as the first element and an iterator to the greatest element as the second. Returns std::make_pair(first, first) if the range is empty. If several elements are equivalent to the smallest element, the iterator to the first such element is returned. If several elements are equivalent to the largest element, the iterator to the last such element is returned.
Complexity
At most max(floor(3/2(N−1)), 0) applications of the predicate, where N = std::distance(first, last).
Possible implementation
| First version |
|---|
template<class ForwardIt> std::pair<ForwardIt, ForwardIt> minmax_element(ForwardIt first, ForwardIt last) { typedef typename std::iterator_traits<ForwardIt>::value_type value_t; return std::minmax_element(first, last, std::less<value_t>()); } |
| Second version |
template<class ForwardIt, class Compare> std::pair<ForwardIt, ForwardIt> minmax_element(ForwardIt first, ForwardIt last, Compare comp) { std::pair<ForwardIt, ForwardIt> result(first, first); if (first == last) return result; if (++first == last) return result; if (comp(*first, *result.first)) { result.second = result.first; result.first = first; } else { result.second = first; } while (++first != last) { ForwardIt i = first; if (++first == last) { if (comp(*i, *result.first)) result.first = i; else if (!(comp(*i, *result.second))) result.second = i; break; } else { if (comp(*first, *i)) { if (comp(*first, *result.first)) result.first = first; if (!(comp(*i, *result.second))) result.second = i; } else { if (comp(*i, *result.first)) result.first = i; if (!(comp(*first, *result.second))) result.second = first; } } } return result; } |
Example
#include <algorithm> #include <iostream> #include <vector> int main() { std::vector<int> v = { 3, 9, 1, 4, 2, 5, 9 }; auto result = std::minmax_element(v.begin(), v.end()); std::cout << "min element at: " << (result.first - v.begin()) << '\n'; std::cout << "max element at: " << (result.second - v.begin()) << '\n'; }
Output:
min element at: 2 max element at: 6
