2990775_ce.cpp

北大大牛代码 1240道题的原代码 超级权威

import java.util.*;

public class Main
{
	public static void main(String [] arvs)
	{
		Scanner cin = new Scanner (System.in);
		int n, k;
		double p, w, t;

		while(true)
		{
			n = cin.nextInt();
			p = cin.nextDouble();
			if(n==0)
				break;
			w = (double)(1<<n);
			for(k = n - 1; k >= 0; k--)
			{
				double kk;
				kk = (double)(1<<k);
				t = kk/w;
				if(p >= t)
					w = (p+1)/2*w;
				else
					w = kk*(t-p)/(1-p) + w*(t+1)/2*(1-t)/(1-p);
			}
			int ans;
			ans = (int)(w*10000);
			if(ans%10 >= 5)
			{
				ans += 10;
			}
			ans /= 10;
			System.out.print(ans/1000);
			System.out.print('.');
			System.out.printf("%03d\n",ans%1000);
		}
	}
}