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#include <cstdlib>
#include <cstring>
#include <iostream>
#include <deque>
using namespace std;
typedef std::deque<int> list_t;
size_t partition(list_t& lst, size_t left, size_t right, size_t pivot)
{
if (left == right)
return left;
list_t::value_type pivot_val = lst[pivot];
swap(lst[pivot], lst[right]); // move pivot to end.
size_t store_pos = left;
for (size_t i = left; i <= right-1; ++i)
{
if (lst[i] < pivot_val)
{
swap(lst[i], lst[store_pos]);
++store_pos;
}
}
swap(lst[store_pos], lst[right]); // Move pivot to its final place.
return store_pos;
}
void quick_sort_run(list_t& lst, size_t left, size_t right)
{
if (left >= right)
return;
if (right - left == 1)
{
// There is only 2 elements.
if (lst[left] > lst[right])
swap(lst[left], lst[right]);
return;
}
// There should be at least 3 elements in this segment.
size_t pivot = right - left == 2 ? left + 1 : (left+right) / 2;
pivot = partition(lst, left, right, pivot);
if (pivot == left)
{
quick_sort_run(lst, left, pivot);
quick_sort_run(lst, pivot+1, right);
}
else
{
quick_sort_run(lst, left, pivot-1);
quick_sort_run(lst, pivot+1, right);
}
}
void quick_sort(list_t& lst)
{
size_t n = lst.size();
if (n <= 1)
// Nothing to do.
return;
quick_sort_run(lst, 0, n-1);
}
void print_list(const list_t& lst, const char* caption)
{
cout << caption << ": ";
for (list_t::const_iterator i = lst.begin(), ie = lst.end(); i != ie; ++i)
cout << *i << " ";
cout << endl;
}
int main(int argc, char** argv)
{
if (argc < 2)
{
cout << "needs at least one argument" << endl;
return EXIT_FAILURE;
}
const char* p = argv[1];
const char* pend = p + strlen(p);
char* endptr = NULL;
long list_size = strtol(p, &endptr, 10);
if (endptr != pend)
{
cout << "invalid number: " << p << endl;
return EXIT_FAILURE;
}
cout << "list size: " << list_size << endl;
list_t lst;
for (int i = 0; i < list_size; ++i)
{
double val = rand();
val /= RAND_MAX;
val *= 100;
lst.push_back(val);
}
print_list(lst, "original");
quick_sort(lst);
print_list(lst, "sorted");
return EXIT_SUCCESS;
}
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