list::sort()

下面是list中的自带的sort，因为list的迭代器是双向迭代器，所有不能使用STL算法中的sort（随机访问迭代器才能）

template <class _Tp, class _Alloc> template <class _StrictWeakOrdering>
void list<_Tp, _Alloc>::sort(_StrictWeakOrdering __comp)
{
  // Do nothing if the list has length 0 or 1.
  if (_M_node->_M_next != _M_node && _M_node->_M_next->_M_next != _M_node) {
    list<_Tp, _Alloc> __carry;
    list<_Tp, _Alloc> __counter[64];
    int __fill = 0;
    while (!empty()) {
      __carry.splice(__carry.begin(), *this, begin());
      int __i = 0;
      while(__i < __fill && !__counter[__i].empty()) {
        __counter[__i].merge(__carry, __comp);
        __carry.swap(__counter[__i++]);
      }
      __carry.swap(__counter[__i]);         
      if (__i == __fill) ++__fill;
    } 

    for (int __i = 1; __i < __fill; ++__i) 
      __counter[__i].merge(__counter[__i-1], __comp);
    swap(__counter[__fill-1]);
  }
}

上面的该算法实际上使用了归并排序的思想，先归并前两个元素，接着归并后两个元素，然后归并前四个元素，然后是8个....,count[i]保存了归并排序的元素，最后将count[i]进行合并

下面是该过程的一个测试，输出了归并的各个阶段的情况

#include <iostream>
#include <string>
#include<list>

using namespace std;


typedef list<int> IList;

void print(const IList& list)
{

	IList::const_iterator ite = list.begin();
	for (; ite != list.end(); ++ite)
	{
		cout << *ite << "  ";
	}
	cout << endl;

}

int main()
{
	IList s;

	s.push_back(7);
	s.push_back(6);
	s.push_back(5);
	s.push_back(4);
	s.push_back(3);
	s.push_back(2);
	s.push_back(1);
	s.push_back(0);

	IList carry;
	IList counter[64];
	int fill = 0;
	int num = 0;
	while (!s.empty())
	{
		cout << "取第" << num << "个数据: fill = " << fill << endl;
		carry.splice(carry.begin(), s, s.begin());  
		int i = 0;
		while (i < fill && !counter[i].empty())
		{
			counter[i].merge(carry);
			carry.swap(counter[i++]);
		}
		carry.swap(counter[i]);
		if (i == fill)
			++fill;
		//我自己加的计数
		num++;

		//打印每次完的结果
		for (int i = 0; i < fill; ++i)
		{
			cout << "count["<<i<<"]==";
			print(counter[i]);
		}
	}

	for (int i = 1; i < fill; ++i)
		counter[i].merge(counter[i - 1]);
	s.swap(counter[fill - 1]);
	for (auto& m : s)
		cout << m << " ";
	return 0;
}