HDU2013 蟠桃记

迭代

#include <iostream>

using namespace std;

int main()
{
	int n;
	while(cin >> n)
	{
		int today = 1;
		int yesterday = 0;
		for(int i=1; i<n; i++)
		{
			yesterday = (today+1)*2;
			today = yesterday;
		}
		cout << yesterday << endl;
	}
	return 0;
}

递归版本

#include <iostream>

using namespace std;

int sum (int n)
{
	if(n == 1)
	{
		return 1;
	}
	else
	{
		return (sum(n-1)+1)*2;
	}
}

int main()
{
	int n;
	while(cin >> n)
	{
		cout << sum(n) << endl;
	}

	return 0;
}