codeforces 677c Vanya and Label
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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 base64 and got new word. Now Vanya thinks of some strings and wants to know the number of pairs of words of length|s| (length of s), such that their bitwise AND is equal tos. As this number can be large, output it modulo109 + 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 from0 to 9;
- letters from 'A' to 'Z' correspond to integers from10 to 35;
- letters from 'a' to 'z' correspond to integers from36 to 61;
- letter '-' correspond to integer 62;
- letter '_' correspond to integer 63.
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 '_'.
Print a single integer — the number of possible pairs of words, such that their bitwise AND is equal to strings modulo 109 + 7.
z
3
V_V
9
Codeforces
130653412
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:
- z&_ = 61&63 = 61 = z
- _&z = 63&61 = 61 = z
- z&z = 61&61 = 61 = z
题意:就是说给你一个字符串,问你有多少个长度和它相同的字符串&后仍然和它等值,
思路:既然长度相同我们可以这样做去求每一个字符有多少个和它&一次值仍等于它,最后再把所有的值累乘不就好了么?关于怎么求每个字符有多少个和它&后值相等的呢?
首先如果是0的话,则有0&0,0&1,1&0三种,如果是1的话,就只有1&1这一种情况,好了,我们的字符在0-63之间,那就是说明每个字符二进制表示有6位呗,然后在对每一位来进行统计就ok了,
AC代码:
#include <iostream>#include <cstring>#include <cstdio>#include <cstdlib>#include <algorithm>#include <cstring>#include <cmath>using namespace std;char c[100005];const int mod = 1000000007;int main() { cin >> c; long long ans = 1; int len = strlen(c); for(int i=0; i<len; i++) { int g; if(c[i]>= '0' && c[i] <= '9') { g = c[i]-'0'; } if(c[i] >= 'A' && c[i] <= 'Z') { g = c[i]-'A'+10; } if(c[i] >= 'a' && c[i] <= 'z') { g = c[i]-'a'+36; } if(c[i] == '-') { g = 62; } if(c[i] == '_') { g = 63; } for(int j = 0; j<6; j++) { if(!((g >> j)&1)) {//右移操作得到的就是第j位是0还是1; ans *= 3; ans %= mod; } } } cout << ans << endl; return 0;}
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