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#include <cstdlib>
#include <cstring>
#include <iostream>
#include <deque>
using namespace std;
typedef std::deque<int> list_t;
void merge(list_t& lst, list_t left, list_t right)
{
list_t res;
while (!left.empty() || !right.empty())
{
if (!left.empty() && !right.empty())
{
if (left.front() <= right.front())
{
res.push_back(left.front());
left.pop_front();
}
else
{
res.push_back(right.front());
right.pop_front();
}
}
else if (!left.empty())
{
res.push_back(left.front());
left.pop_front();
}
else if (!right.empty())
{
res.push_back(right.front());
right.pop_front();
}
}
res.swap(lst);
}
void merge_sort(list_t& lst)
{
size_t n = lst.size();
if (n <= 1)
return;
list_t left, right;
size_t mpos = n / 2;
for (size_t i = 0; i < n; ++i)
{
if (i < mpos)
left.push_back(lst[i]);
else
right.push_back(lst[i]);
}
merge_sort(left);
merge_sort(right);
merge(lst, left, right);
}
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 *= 50;
lst.push_back(val);
}
print_list(lst, "original");
merge_sort(lst);
print_list(lst, "sorted");
return EXIT_SUCCESS;
}
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