Codeforces

476b.cpp

#include <cmath>
#include <iomanip>
#include <iostream>
using namespace std;

int main(void)
{
    string s1, s2;
    cin >> s1 >> s2;

    int n = s1.length();       // length of the signal
    int p1 = 0, m1 = 0;        // count of plus and minus in s1
    int p2 = 0, m2 = 0, q = 0; // count of plus, minus, and unrecognized in s2

    for (auto c : s1)
        if (c == '+')
            p1++;
        else
            m1++;

    for (auto c : s2)
        if (c == '+')
            p2++;
        else if (c == '-')
            m2++;
        else
            q++;

    if (p2 + m2 == n)
    { // all commands are recognized
        if (p1 - m1 == p2 - m2)
            cout << 1.0 << endl;
        else
            cout << 0.0 << endl;
    }
    else
    { // some commands are not recognized
        int d = abs(p1 - m1 - p2 + m2);

        if (d > q || (d % 2 != q % 2))
            cout << 0.0 << endl;
        else
        {
            int x = (q - d) / 2;
            double denominator = pow(2, q);

            double numerator = 1; // Combination(q, x)
            for (int i = 0; i < x; i++)
            {
                numerator *= q - i;
                numerator /= i + 1;
            }

            cout.precision(10);
            cout << numerator / denominator << endl;
        }
    }
}