CodeForces - 476B -Dreamoon and WiFi（DFS+概率思维）-优快云博客

本文探讨了一个有趣的问题，即Dreamoon如何根据Drazil通过Wi-Fi发送的指令，在信号不佳的情况下，利用智能手机识别并执行命令，到达预设的目标位置。文章详细介绍了输入输出格式，通过实例解释了如何计算Dreamoon最终到达正确位置的概率，并提供了一段C++代码实现。

Dreamoon is standing at the position 0 on a number line. Drazil is sending a list of commands through Wi-Fi to Dreamoon's smartphone and Dreamoon follows them.

Each command is one of the following two types:

Go 1 unit towards the positive direction, denoted as '+'
Go 1 unit towards the negative direction, denoted as '-'

But the Wi-Fi condition is so poor that Dreamoon's smartphone reports some of the commands can't be recognized and Dreamoon knows that some of them might even be wrong though successfully recognized. Dreamoon decides to follow every recognized command and toss a fair coin to decide those unrecognized ones (that means, he moves to the 1 unit to the negative or positive direction with the same probability 0.5).

You are given an original list of commands sent by Drazil and list received by Dreamoon. What is the probability that Dreamoon ends in the position originally supposed to be final by Drazil's commands?

Input

The first line contains a string s1 — the commands Drazil sends to Dreamoon, this string consists of only the characters in the set {'+', '-'}.

The second line contains a string s2 — the commands Dreamoon's smartphone recognizes, this string consists of only the characters in the set {'+', '-', '?'}. '?' denotes an unrecognized command.

Lengths of two strings are equal and do not exceed 10.

Output

Output a single real number corresponding to the probability. The answer will be considered correct if its relative or absolute error doesn't exceed 10 - 9.

Examples

Input

++-+-
+-+-+

Output

1.000000000000

Input

+-+-
+-??

Output

0.500000000000

Input

+++
??-

Output

0.000000000000

Note

For the first sample, both s1 and s2 will lead Dreamoon to finish at the same position + 1.

For the second sample, s1 will lead Dreamoon to finish at position 0, while there are four possibilites for s2: {"+-++", "+-+-", "+--+", "+---"} with ending position {+2, 0, 0, -2} respectively. So there are 2 correct cases out of 4, so the probability of finishing at the correct position is 0.5.

For the third sample, s2 could only lead us to finish at positions {+1, -1, -3}, so the probability to finish at the correct position + 3 is 0.

思路：将？号部分进行dfs暴搜，然后去比较是否相等和sum1相等，相等s就加1，每次有问号会产生2的问号个数次方的情况，最后进行概率的转化即可

代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>

using namespace std;
	int sum1=0;
	int sum2=0;
	int sum3=0;
	int s=0;
void dfs(int s1,int x)
{
	
	if(s1==0)
	{
		if(x==sum1)
	    s++;
		return ;
	}
	
	dfs(s1-1,x+1);
	dfs(s1-1,x-1);
	
}
int main()
{
	
	string str1,str2;
	cin>>str1>>str2;

	
	for(int t=0;t<str1.length();t++)
	{
		if(str1[t]=='+')
		{
			sum1+=1;
	    }
	    if(str1[t]=='-')
	    {
	    	sum1--;
		}
	}
	for(int t=0;t<str2.length();t++)
	{
		if(str2[t]=='+')
		{
			sum2++;
		}
		if(str2[t]=='-')
		{
			sum2--;
		}
		if(str2[t]=='?')
		{
			sum3++;
		}
	}
	int k=sum3;
	if(sum3==0)
	{
		if(sum2==sum1)
		{
			printf("1.000000000000\n");
		}
		else
		{
			printf("0.000000000000\n");
		}
	}
	else
	{
		dfs(sum3,sum2);
		double ss=s*1.0/pow(2,k);
		printf("%.12f\n",ss);
	}
	
	
	
	return 0;
}

转载于:https://www.cnblogs.com/Staceyacm/p/10781843.html