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AK: Simplify quick_sort() and improve Vector iterators a bit.

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This commit is contained in:
Andreas Kling 2019-05-19 01:53:51 +02:00
parent 853597200e
commit 6e305bf838
Notes: sideshowbarker 2024-07-19 14:01:43 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/6e305bf838e
2 changed files with 24 additions and 30 deletions
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52
AK/QuickSort.h
View file

@ -2,44 +2,36 @@
namespace AK {
template<typename IteratorType, typename LessThan>
IteratorType partition(IteratorType first, IteratorType last, LessThan less_than)
{
auto pivot = last;
auto smallest = first - 1;
auto it = first;
for (; it < last; ++it) {
if (less_than(*it, *pivot)) {
++smallest;
swap(*it, *smallest);
}
}
swap(*(smallest + 1), *last);
return smallest + 1;
}
template<typename IteratorType, typename LessThan>
void quick_sort_impl(IteratorType begin, IteratorType first, IteratorType last, LessThan less_than)
{
if (first < last) {
auto pivot = partition(first, last, less_than);
quick_sort_impl(begin, first, pivot - 1, less_than);
quick_sort_impl(begin, pivot + 1, last, less_than);
}
}
template<typename T>
bool is_less_than(const T& a, const T& b)
{
return a < b;
}
template<typename IteratorType, typename LessThan>
void quick_sort(IteratorType begin, IteratorType end, LessThan less_than = is_less_than)
template <typename Iterator, typename LessThan>
void quick_sort(Iterator start, Iterator end, LessThan less_than = is_less_than)
{
if (begin == end)
int size = end - start;
if (size <= 0)
return;
quick_sort_impl(begin, begin, end - 1, less_than);
int pivot_point = size / 2;
auto pivot = *(start + pivot_point);
if (pivot_point)
swap(*(start + pivot_point), *start);
int i = 1;
for (int j = 1; j < size; ++j) {
if (less_than(*(start + j), pivot)) {
swap(*(start+j), *(start + i));
++i;
}
}
swap(*start, *(start + i - 1));
quick_sort(start, start + i - 1, less_than);
quick_sort(start + i, end, less_than);
}
}

2
AK/Vector.h
View file

@ -316,6 +316,7 @@ public:
Iterator operator-(int value) { return { m_vector, m_index - value }; }
Iterator operator+(int value) { return { m_vector, m_index + value }; }
T& operator*() { return m_vector[m_index]; }
int operator-(const Iterator& other) { return m_index - other.m_index; }
private:
friend class Vector;
Iterator(Vector& vector, int index) : m_vector(vector), m_index(index) { }
@ -335,6 +336,7 @@ public:
ConstIterator operator-(int value) { return { m_vector, m_index - value }; }
ConstIterator operator+(int value) { return { m_vector, m_index + value }; }
const T& operator*() const { return m_vector[m_index]; }
int operator-(const ConstIterator& other) { return m_index - other.m_index; }
private:
friend class Vector;
ConstIterator(const Vector& vector, const int index) : m_vector(vector), m_index(index) { }