题目链接：https://codeforces.com/contest/383/problem/E

1 题目大意

给定 $n$ 个长度为 $3$，字符集为 a-x 的字符串。

对于 $s, s \subseteq [ \texttt{a}, \texttt{x} ]$，有 $f(s)$ 表示有多少个给定字符串和 $s$ 交集非空。

输出 $\sum^{\oplus}_s f(s) * f(s)$

2 思路

注意到基本上是 SOS DP 的模版，除一个问题 — 对于一个字符串可能会被统计多次。

简单容斥即可。

3 Code

/*
 * e.cpp
 * Copyright (C) 2022 Woshiluo Luo <[email protected]>
 *
 * 「Two roads diverged in a wood,and I—
 * I took the one less traveled by,
 * And that has made all the difference.」
 *
 * Distributed under terms of the GNU AGPLv3+ license.
 */

#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <vector>
#include <algorithm>

typedef long long ll;
typedef unsigned long long ull;

inline bool isdigit( const char cur ) { return cur >= '0' && cur <= '9'; }/*{{{*/
template <class T> 
T Max( T a, T b ) { return a > b? a: b; }
template <class T> 
T Min( T a, T b ) { return a < b? a: b; }
template <class T> 
void chk_Max( T &a, T b ) { if( b > a ) a = b; }
template <class T> 
void chk_Min( T &a, T b ) { if( b < a ) a = b; }
template <typename T>
T read() { 
    T sum = 0, fl = 1; 
    char ch = getchar();
    for (; isdigit(ch) == 0; ch = getchar())
        if (ch == '-') fl = -1;
    for (; isdigit(ch); ch = getchar()) sum = sum * 10 + ch - '0';
    return sum * fl;
}
template <class T> 
T pow( T a, int p ) {
    T res = 1;
    while( p ) {
        if( p & 1 ) 
            res = res * a;
        a = a * a;
        p >>= 1;
    }
    return res;
}/*}}}*/

int full_pow( const int cur ) { return 1 << cur; }
bool chk_pos( const int cur, const int p ) { return cur & full_pow(p); }

const int K = 24;
const int N = ( 1 << K ) + 10;

int f[N];

int main() {
#ifdef woshiluo
    freopen( "e.in", "r", stdin );
    freopen( "e.out", "w", stdout );
#endif
    const int n = read<int>();
    for( int i = 1; i <= n; i ++ ) {
        static char str[10];
        scanf( "%s", str + 1 );
        std::vector<int> a;
        for( int j = 1; j <= 3; j ++ )
            a.push_back( str[j] - 'a' );

        std::sort( a.begin(), a.end() );
        a.erase( std::unique( a.begin(), a.end() ), a.end() );
        const int size = a.size();
        for( int st = 1; st < full_pow(size); st ++ ) {
            int mask = 0, cnt = 0;
            for( int j = 0; j < size; j ++ ) {
                if( chk_pos( st, j ) ) {
                    cnt ++;
                    mask |= full_pow( a[j] );
                }
            }
            f[mask] += ( ( cnt & 1 ) ? 1: -1 );
        }
    }
    for( int j = 0; j < K; j ++ ) 
        for( int st = 0; st < full_pow(K); st ++ ) 
            if( chk_pos( st, j ) )
                f[st] += f[ st ^ full_pow(j) ];

    int ans = 0;
    for( int st = 0; st < full_pow(K); st ++ ) 
        ans ^= ( f[st] * f[st] );
    printf( "%d\n", ans );
}