第一题：一个人上台阶可以一次上1个，2个，或者3个，问这个人上n层的台阶，总共有几种走法？

第一题：一个人上台阶可以一次上1个，2个，或者3个，问这个人上n层的台阶，总共有几种走法？

void print(int x)
{
	printf("%d ", x);
}
void louti(int n)
{
	vector<char> sk;
	sk.push_back(1);
	int cur_stair = 1;
	while(true){
		if(cur_stair > n || sk[sk.size()-1] == 4){
			cur_stair -= sk[sk.size()-1];
			sk.pop_back();
			if(sk.empty ())
				break;
			sk[sk.size()-1]++;
			cur_stair++;
			continue;
		}
		if(cur_stair == n){
			for_each(sk.begin(), sk.end(), print);
			printf("\n");
			cur_stair += 4-sk[sk.size() - 1];
			sk[sk.size() - 1] = 4;
			continue;
		}
		cur_stair++;
		sk.push_back (1);
	}	
}

int louti_r(int n, bool first)
{
	static vector<char> sk;
	static int cur_stair = 0;
	static int count = 0;//计数总的方案数
	if(first == true){
		sk.clear();
		cur_stair = 0;
		count = 0;
	}
	if(cur_stair > n){
		return count;
	}else if(cur_stair == n){
		count++;
		for_each(sk.begin(), sk.end(), print);
		printf("\n");
		return count;
	}
	for(int i = 1; i < 4; i++){
		sk.push_back (i);
		cur_stair += i;
		louti_r(n, false);
		cur_stair -= i;
		sk.pop_back ();
	}
	return count;
}