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

Three-valued logic is a logic system that has, in addition to "true" and
"false", "unknown" as a valid value.

In the following, logical values "false", "unknown" and "true" are
represented by 0, 1 and 2 respectively.

Let "-" be a unary operator (i.e. a symbol representing one argument function)
and let both "*" and "+" be binary operators (i.e. symbols representing
two argument functions).
These operators represent negation (NOT), conjunction (AND) and
disjunction (OR) respectively.
These operators in three-valued logic can be defined in Table C-1.

Table C-1: Truth tables of three-valued logic operators

-X

(X*Y)

(X+Y)

Let P, Q and R be variables ranging over three-valued logic values.
For a given formula, you are asked to answer the number of triples (P,Q,R)
that satisfy the formula, that is, those which make the value of the
given formula 2.
A formula is one of the following form (X and Y represent formulas).

Constants: 0, 1 or 2

Variables: P, Q or R

Negations: -X

Conjunctions: (X*Y)

Disjunctions: (X+Y)

Note that conjunctions and disjunctions of two formulas are always
parenthesized.

For example, when formula (P*Q) is given as an input, the value of
this formula is 2 when and only when (P,Q,R) is (2,2,0), (2,2,1) or (2,2,2).
Therefore, you should output 3.

Input

The input consists of one or more lines. Each line contains a formula.
A formula is a string which consists of 0, 1, 2, P, Q, R, -, *, +, (, ).
Other characters such as spaces are not contained.
The grammar of formulas is given by the following BNF.

<formula> ::= 0 | 1 | 2 | P | Q | R |
-<formula> | (<formula>*<formula>) | (<formula>+<formula>)

All the formulas obey this syntax and thus you do not have to care about
grammatical errors.
Input lines never exceed 80 characters.

Finally, a line which
contains only a "." (period) comes, indicating the end of the input.

Output

You should answer the number (in decimal) of triples (P,Q,R) that make the
value of the given formula 2. One line containing the number should be
output for each of the formulas, and no other characters should be output.

Sample Input

(P*Q)
(--R+(P*Q))
(P*-P)
2
1
(-1+(((---P+Q)*(--Q+---R))*(-R+-P)))
.

Output for the Sample Input

3
11
0
27
0
7

Solution in C# (judge verdict: Accepted)

using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Trace;
using SB = System.Text.StringBuilder;
using Number = System.Int64;
namespace Program
{
    public class Solver
    {
        public void Solve()
        {
            for (; ; )
            {
                var s = sc.ScanLine();
                if (s == ".") return;
                Debug.WriteLine(s);
                var ans = 0;
                for (a[0] = 0; a[0] < 3; a[0]++)
                    for (a[1] = 0; a[1] < 3; a[1]++)
                        for (a[2] = 0; a[2] < 3; a[2]++)
                        {
                            if (parse(s) == 2) ans++;
                        }
                Console.WriteLine(ans);

            }
        }
        int[] a = new int[3];
        const string S = "PQR";
        int parse(string s)
        {
            int ptr = 0;
            return expression(s, ref ptr);
        }
        int expression(string s, ref int ptr)
        {
            if (s[ptr] == '(')
            {
                ptr++;
                var x = expression(s, ref ptr);
                var c = s[ptr++];
                var y = expression(s, ref ptr);
                if (x > y) Swap(ref x, ref y);
                if (c == '*')
                {
                    if (x * y == 4) x = 2;
                    else if (x * y != 0) x = 1;
                    else x = 0;

                }
                else
                {
                    if (y == 0) x = 0;
                    else if (y == 1) x = 1;
                    else x = 2;
                }
                ptr++;
                return x;
            }
            return token(s, ref ptr);
        }
        int token(string s, ref int ptr)
        {
            if (s[ptr] == '-') { ptr++; return 2 - expression(s, ref ptr); }
            if (char.IsDigit(s[ptr])) return s[ptr++] - '0';
            else return a[S.IndexOf(s[ptr++])];

        }
        const long INF = 1L << 60;
        //int[] dx = { -1, 0, 1, 0 };
        //int[] dy = { 0, 1, 0, -1 };
        //*
        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        //*/

        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex
{
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ")
    {
        return string.Join(st, ie.Select(x => x.ToString()).ToArray());
        //return string.Join(st, ie);
    }
    static public void Main()
    {
        Console.SetOut(new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer: StreamWriter
    {
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }
    public class StreamScanner
    {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read()
        {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read())
                if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}
#endregion