高效Permutation算法

class FastPermutation
{
public:
	typedef function ENUMERATOR;
	static void Enum(int base, ENUMERATOR enumerator)
	{
		FastPermutation permutation;
		permutation.CalculateAtLevel(base, enumerator);
	}

private:
	void CalculateAtLevel(int level, ENUMERATOR enumerator)
	{
		if (level == 1)
		{
			int sequence[] = { 0 };
			enumerator(sequence);
			return;
		}

		int* sequence = new int[level];
		this->





CalculateAtLevel(level - 1, [level, sequence, enumerator](int* s)
		{
			int* key = sequence + (level - 1);
			*key = level - 1;
			for (int i = 0; i < level - 1; i++) sequence[i] = s[i];
			
			enumerator(sequence);
			while (key != sequence)
			{
				*key = *(key - 1);
				*(--key) = level - 1;
				enumerator(sequence);
			}
		});
		delete[] sequence;
	}
};