How can I satisfy thee? Let me count the ways...

http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1155

001 #include<iostream>
002 #include<string>
003 #include<map>
004 #include<cassert>
005 using namespace std;
006 
007 map<char, int> V;
008 string exp;
009 int pos;
010 
011 int formula(){
012     char ch = exp[pos];
013     if ( isdigit(ch) ){
014         pos++; return ch - '0';
015     } else if ( isalpha(ch) ){
016         pos++; return V[ch];
017     } else if ( ch == '-' ){
018         pos++; return (2 - formula()); // NOT
019     } else if ( ch == '(' ){
020         int v1, v2;
021         char op;
022         pos++;
023         v1 = formula();
024         op = exp[pos++];
025         v2 = formula();
026         assert( exp[pos++] == ')');
027         if ( op == '*' ) return min( v1, v2 ); // AND
028         else if ( op == '+' ) return max( v1, v2 ); // OR
029     }
030 }
031 
032 main(){
033     int cnt;
034     while( cin >> exp && exp != "."){
035         cnt = 0;
036         for ( int p = 0; p <= 2; p++ ){
037             for ( int q = 0; q <= 2; q++ ){
038                 for ( int r = 0; r <= 2; r++ ){
039                     V['P'] = p;
040                     V['Q'] = q;
041                     V['R'] = r;
042                     pos = 0;
043                     if ( formula() == 2 ) cnt++;
044                 }
045             }
046         }
047         cout << cnt << endl;
048     }
049 }