[英]Insertion sort implementation using iterators and vectors
I'm trying to implement insertion sort algorithm using iterators and it doesn't seem to work as I thought... Do you have any ideas of how to implement it?我正在尝试使用迭代器实现插入排序算法,但它似乎并没有像我想象的那样工作......你对如何实现它有任何想法吗?
Also, I can't use code like this one: https://www.geeksforgeeks.org/insertion-sort-using-c-stl/ because I'm intending to make an animation and it will get more complicated.另外,我不能使用这样的代码: https://www.geeksforgeeks.org/insertion-sort-using-c-stl/因为我打算制作一个 animation,它会变得更加复杂。
This is my source code so far:到目前为止,这是我的源代码:
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
std::vector<int> seq = { 5, 4, 3, 2, 1 };
std::vector<int>::iterator itj;
std::vector<int>::iterator leftmost;
// insertion sort
for (std::vector<int>::iterator iti = seq.begin() + 1; iti != seq.end(); iti = std::next(iti))
{
itj = std::prev(iti);
leftmost = iti;
while (std::distance(seq.begin(), itj) >= 0 && *itj > *leftmost)
{
std::next(itj) = itj;
itj = prev(itj);
}
std::next(itj) = leftmost;
}
// printing
for (std::vector<int>::iterator iti = seq.begin(); iti != seq.end(); iti = std::next(iti))
{
std::cout << *iti << " ";
}
}
Here's a very elegant implementation of insertion sort using iterators lifted directly from the reference page on rotate :这是一个非常优雅的插入排序实现,它使用直接从rotate上的参考页面提升的迭代器:
// insertion sort
for (auto i = v.begin(); i != v.end(); ++i) {
std::rotate(std::upper_bound(v.begin(), i, *i), i, i+1);
}
All you have to do is understand how std::rotate
works, and this becomes easy to understand.您所要做的就是了解
std::rotate
是如何工作的,这很容易理解。 ( rotate
is anyway a really powerful algorithm that you should be comfortable with). (无论如何,
rotate
是一个非常强大的算法,你应该感到舒服)。
Here is animplementation taken from SGI STL 1 :这是取自 SGI STL 1的实现:
template<class Random_it, class T>
void unguarded_linear_insert(Random_it last, T val) {
auto next = last;
--next;
while (val < *next) {
*last = *next;
last = next;
--next;
}
*last = val;
}
template<class Random_it>
void linear_insert(Random_it first, Random_it last) {
auto val = *last;
if (val < *first) {
std::copy_backward(first, last, last + 1);
*first = val;
}
else
unguarded_linear_insert(last, val);
}
template<class Random_it>
void insertion_sort(Random_it first, Random_it last) {
if (first == last)
return;
for (auto i = first + 1; i != last; ++i)
linear_insert(first, i);
}
Note how the val < *first
condition and std::copy_backward
are used to simplify the loop inside unguarded_linear_insert
: only one condition, namely val < *next
can be checked in that loop.请注意如何使用
val < *first
条件和std::copy_backward
来简化unguarded_linear_insert
内的循环:在该循环中只能检查一个条件,即val < *next
。
1 The same implementation can be found in libstdc++. 1在 libstdc++ 中可以找到相同的实现。
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