poj 3678 2-sat

  1 #include <algorithm>
  2 #include <iostream>
  3 #include <cstring>
  4 #include <cstdio>
  5 using namespace std;
  6 
  7 const int N = 1000;
  8 const int M = 5000000;
  9 int head[N * 2];
 10 int s[N * 2];
 11 bool mark[N * 2];
 12 int n, m, e, c;
 13 
 14 struct Edge
 15 {
 16     int v, next;
 17 } edge[M];
 18 
 19 void addEdge( int u, int v )
 20 {
 21     edge[e].v = v;
 22     edge[e].next = head[u];
 23     head[u] = e++;
 24 }
 25 
 26 void init()
 27 {
 28     e = 0;
 29     memset( head, -1, sizeof(head) );
 30     memset( mark, false, sizeof(mark) );
 31 }
 32 
 33 bool dfs( int u )
 34 {
 35     if ( mark[u ^ 1] ) return false;
 36     if ( mark[u] ) return true;
 37     mark[u] = true;
 38     s[c++] = u;
 39     for ( int i = head[u]; i != -1; i = edge[i].next )
 40     {
 41         int v = edge[i].v;
 42         if ( !dfs(v) ) return false;
 43     }
 44     return true;
 45 }
 46 
 47 bool solve()
 48 {
 49     for ( int i = 0; i < 2 * n; i += 2 )
 50     {
 51         if ( !mark[i] && !mark[i + 1] )
 52         {
 53             c = 0;
 54             if ( !dfs(i) )
 55             {
 56                 while ( c )
 57                 {
 58                     c--;
 59                     mark[s[c]] = false;
 60                 }
 61                 if ( !dfs( i + 1 ) ) return false;
 62             }
 63         }
 64     }
 65     return true;
 66 }
 67 
 68 int main ()
 69 {
 70     while ( scanf("%d%d", &n, &m) != EOF )
 71     {
 72         init();
 73         int x, y, z;
 74         char op[11];
 75         while ( m-- )
 76         {
 77             scanf("%d%d%d%s", &x, &y, &z, op);
 78             x = x << 1, y = y << 1;
 79             if ( op[0] == ‘A‘ )
 80             {
 81                 if ( z == 0 )
 82                 {
 83                     addEdge( x ^ 1, y );
 84                     addEdge( y ^ 1, x );
 85                 }
 86                 else
 87                 {
 88                     addEdge( x, x ^ 1 );
 89                     addEdge( y, y ^ 1 );
 90                 }
 91             }
 92             else if ( op[0] == ‘O‘ )
 93             {
 94                 if ( z == 0 )
 95                 {
 96                     addEdge( x ^ 1, x );
 97                     addEdge( y ^ 1, y );
 98                 }
 99                 else
100                 {
101                     addEdge( x, y ^ 1 );
102                     addEdge( y, x ^ 1 );
103                 }
104             }
105             else if ( op[0] == ‘X‘ )
106             {
107                 if ( z == 0 )
108                 {
109                     addEdge( x, y );
110                     addEdge( x ^ 1, y ^ 1 );
111                     addEdge( y, x );
112                     addEdge( y ^ 1, x ^ 1 );
113                 }
114                 else
115                 {
116                     addEdge( x, y ^ 1 );
117                     addEdge( x ^ 1, y );
118                     addEdge( y, x ^ 1 );
119                     addEdge( y ^ 1, x );
120                 }
121             }
122         }
123         if ( solve() )
124         {
125             printf("YES\n");
126         }
127         else
128         {
129             printf("NO\n");
130         }
131     }
132     return 0;
133 }