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  • Codeforces 677C. Vanya and Label 位操作

    C. Vanya and Label
    time limit per test:1 second
    memory limit per test:256 megabytes
    input:standard input
    output:standard output

    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
     
    传送门:http://codeforces.com/contest/677/problem/C

    题意:一个字符串s,字符串的每个字母代表一种数字。问多少种的等长的字符串通过&操作得到s。

    思路:1&0=0,0&1=0,0&0=0,1&1=1。字符串里面的每一个字符ch的每一位与1 &操作,如果得到0就有3就情况,如果得到1只有一种情况。[0,63]的2进制最多有6位。

    代码:

    #include<bits/stdc++.h>
    using namespace std;
    const int mod = 1e9+7;
    char s[100100];
    int getidx(char c)
    {
        if(c>='0'&&c<='9') return c-'0';
        if(c>='A'&&c<='Z') return c-'A'+10;
        if(c>='a'&&c<='z') return c-'a'+36;
        if(c=='-') return 62;
        if(c=='_') return 63;
    }
    int main()
    {
        int i,j;
        scanf("%s",s);
        __int64 ans = 1;
        for(i=0; i<strlen(s); i++)
        {
            int p = getidx(s[i]);
            for(j=0; j<6; j++)
                if(((p>>j)&1)==0) ans=ans*3%mod;
        }
        cout<<ans<<endl;
    }
    位操作
    I am a slow walker,but I never walk backwards.
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  • 原文地址:https://www.cnblogs.com/GeekZRF/p/5735994.html
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