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  • CodeForce 677C

    Vanya and Label

    While walking down the street Vanya saw a label "Hide&Seek". Because he is a programmer, he used & as a bitwise AND for these two words represented as a integers in base 64 and got new word. Now Vanya thinks of some string s and wants to know the number of pairs of words of length |s| (length of s), such that their bitwise AND is equal to s. As this number can be large, output it modulo 109 + 7.

    To represent the string as a number in numeral system with base 64 Vanya uses the following rules:

    • digits from '0' to '9' correspond to integers from 0 to 9;
    • letters from 'A' to 'Z' correspond to integers from 10 to 35;
    • letters from 'a' to 'z' correspond to integers from 36 to 61;
    • letter '-' correspond to integer 62;
    • letter '_' correspond to integer 63.
    Input

    The only line of the input contains a single word s (1 ≤ |s| ≤ 100 000), consisting of digits, lowercase and uppercase English letters, characters '-' and '_'.

    Output

    Print a single integer — the number of possible pairs of words, such that their bitwise AND is equal to string s modulo 109 + 7.

    Examples
    Input
    z
    Output
    3
    Input
    V_V
    Output
    9
    Input
    Codeforces
    Output
    130653412
    Note

    For a detailed definition of bitwise AND we recommend to take a look in the corresponding article in Wikipedia.

    In the first sample, there are 3 possible solutions:

    1. z&_ = 61&63 = 61 = z
    2. _&z = 63&61 = 61 = z
    3. z&z = 61&61 = 61 = z

    题意:

      给出字符串转化为数字,问有多少个 位 & 还是原来的数字

    思路:

      把这些字符转化成数字后变成2进制,看有多少个0,如果有n个0,那么就是3的n次方;
      因为每一个为0的位置上可以有0&1,1&0,0&0,这3种情况,最后结果就是3的n次方了,快速幂

    AC代码:
    # include <iostream>
    using namespace std;
    const int mod = 1e9+7;
    string s;
    int f(char ch)
    {
        if(ch >= '0' && ch <= '9')
    		return ch - '0';
        else if(ch >= 'A' && ch <= 'Z')
    		return ch-'A'+10;
        else if(ch >= 'a' && ch <= 'z')
    		return ch - 'a' + 36;
        else if(ch == '-')
    		return 62;
        else if(ch == '_')
    		return 63;
    }
    int main()
    {
        cin >> s;
        long long ans = 1;
        for(int i = 0; i < s.size();i++)
        {
            int t = f(s[i]);
            for(int j = 0; j < 6; j++)
                if(!((t >> j) & 1 ))
    				ans = ans * 3 % mod;   
        }
        cout << ans << endl;
    }
    
    
    
    
     
    生命不息,奋斗不止,这才叫青春,青春就是拥有热情相信未来。
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  • 原文地址:https://www.cnblogs.com/lyf-acm/p/5786761.html
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