poj 2570 floyd+二进制

二进制真的是个神奇的东西！

类似floyd求传递闭包，这里g[i][j]表示i点到j点的状态（即符合条件的公司的集合）。

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

const int N = 201;
const int M = 31;
int g[N][N];
int n;

int main ()
{
    while ( scanf("%d", &n), n )
    {
        memset( g, 0, sizeof(g) );
        int u, v;
        char str[M];
        while ( scanf("%d%d", &u, &v) != EOF )
        {
            if ( !u && !v ) break;
            scanf("%s", str);
            int len = strlen(str);
            for ( int i = 0; i < len; i++ )
            {
                int tmp = str[i] - 'a';
                g[u][v] |= ( 1 << tmp );
            }
        }
        for ( int k = 1; k <= n; k++ )
        {
            for ( int i = 1; i <= n; i++ )
            {
                for ( int j = 1; j <= n; j++ )
                {
                    g[i][j] |= ( g[i][k] & g[k][j] );
                }
            }
        }
        int p, q;
        while ( scanf("%d%d", &p, &q) != EOF )
        {
            if ( !p && !q ) break;
            if ( !g[p][q] ) 
            {
                putchar('-');
            }
            else
            {
                for ( int i = 0; ( 1 << i ) <= g[p][q]; i++ )
                {
                    if ( g[p][q] & ( 1 << i ) )
                    {
                        putchar( 'a' + i );
                    }
                }
            }
            putchar('
');
        }
        putchar('
');
    }
    return 0;
}