Task: Chemical calculator



C#: using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ChemicalCalculator {
    class Program {
        static Dictionary<string, double> atomicMass = new Dictionary<string, double>() {
            {"H",     1.008 },
            {"He",    4.002602},
            {"Li",    6.94},
            {"Be",    9.0121831},
            {"B",    10.81},
            {"C",    12.011},
            {"N",    14.007},
            {"O",    15.999},
            {"F",    18.998403163},
            {"Ne",   20.1797},
            {"Na",   22.98976928},
            {"Mg",   24.305},
            {"Al",   26.9815385},
            {"Si",   28.085},
            {"P",    30.973761998},
            {"S",    32.06},
            {"Cl",   35.45},
            {"Ar",   39.948},
            {"K",    39.0983},
            {"Ca",   40.078},
            {"Sc",   44.955908},
            {"Ti",   47.867},
            {"V",    50.9415},
            {"Cr",   51.9961},
            {"Mn",   54.938044},
            {"Fe",   55.845},
            {"Co",   58.933194},
            {"Ni",   58.6934},
            {"Cu",   63.546},
            {"Zn",   65.38},
            {"Ga",   69.723},
            {"Ge",   72.630},
            {"As",   74.921595},
            {"Se",   78.971},
            {"Br",   79.904},
            {"Kr",   83.798},
            {"Rb",   85.4678},
            {"Sr",   87.62},
            {"Y",    88.90584},
            {"Zr",   91.224},
            {"Nb",   92.90637},
            {"Mo",   95.95},
            {"Ru",  101.07},
            {"Rh",  102.90550},
            {"Pd",  106.42},
            {"Ag",  107.8682},
            {"Cd",  112.414},
            {"In",  114.818},
            {"Sn",  118.710},
            {"Sb",  121.760},
            {"Te",  127.60},
            {"I",   126.90447},
            {"Xe",  131.293},
            {"Cs",  132.90545196},
            {"Ba",  137.327},
            {"La",  138.90547},
            {"Ce",  140.116},
            {"Pr",  140.90766},
            {"Nd",  144.242},
            {"Pm",  145},
            {"Sm",  150.36},
            {"Eu",  151.964},
            {"Gd",  157.25},
            {"Tb",  158.92535},
            {"Dy",  162.500},
            {"Ho",  164.93033},
            {"Er",  167.259},
            {"Tm",  168.93422},
            {"Yb",  173.054},
            {"Lu",  174.9668},
            {"Hf",  178.49},
            {"Ta",  180.94788},
            {"W",   183.84},
            {"Re",  186.207},
            {"Os",  190.23},
            {"Ir",  192.217},
            {"Pt",  195.084},
            {"Au",  196.966569},
            {"Hg",  200.592},
            {"Tl",  204.38},
            {"Pb",  207.2},
            {"Bi",  208.98040},
            {"Po",  209},
            {"At",  210},
            {"Rn",  222},
            {"Fr",  223},
            {"Ra",  226},
            {"Ac",  227},
            {"Th",  232.0377},
            {"Pa",  231.03588},
            {"U",   238.02891},
            {"Np",  237},
            {"Pu",  244},
            {"Am",  243},
            {"Cm",  247},
            {"Bk",  247},
            {"Cf",  251},
            {"Es",  252},
            {"Fm",  257},
            {"Uue", 315},
            {"Ubn", 299},
        };

        static double Evaluate(string s) {
            s += "[";
            double sum = 0.0;
            string symbol = "";
            string number = "";
            for (int i = 0; i < s.Length; ++i) {
                var c = s[i];
                if ('@' <= c && c <= '[') {
                    
                    int n = 1;
                    if (number != "") {
                        n = int.Parse(number);
                    }
                    if (symbol != "") {
                        sum += atomicMass[symbol] * n;
                    }
                    if (c == '[') {
                        break;
                    }
                    symbol = c.ToString();
                    number = "";
                } else if ('a' <= c && c <= 'z') {
                    symbol += c;
                } else if ('0' <= c && c <= '9') {
                    number += c;
                } else {
                    throw new Exception(string.Format("Unexpected symbol {0} in molecule", c));
                }
            }
            return sum;
        }

        
        static string ReplaceFirst(string text, string search, string replace) {
            int pos = text.IndexOf(search);
            if (pos < 0) {
                return text;
            }
            return text.Substring(0, pos) + replace + text.Substring(pos + search.Length);
        }

        static string ReplaceParens(string s) {
            char letter = 's';
            while (true) {
                var start = s.IndexOf('(');
                if (start == -1) {
                    break;
                }

                for (int i = start + 1; i < s.Length; ++i) {
                    if (s[i] == ')') {
                        var expr = s.Substring(start + 1, i - start - 1);
                        var symbol = string.Format("@{0}", letter);
                        s = ReplaceFirst(s, s.Substring(start, i + 1 - start), symbol);
                        atomicMass[symbol] = Evaluate(expr);
                        letter++;
                        break;
                    }
                    if (s[i] == '(') {
                        start = i;
                        continue;
                    }
                }
            }
            return s;
        }

        static void Main() {
            var molecules = new string[]{
                "H", "H2", "H2O", "H2O2", "(HO)2", "Na2SO4", "C6H12",
                "COOH(C(CH3)2)3CH3", "C6H4O2(OH)4", "C27H46O", "Uue"
            };
            foreach (var molecule in molecules) {
                var mass = Evaluate(ReplaceParens(molecule));
                Console.WriteLine("{0,17} -> {1,7:0.000}", molecule, mass);
            }
        }
    }
}





Python: assert   1.008 == molar_mass('H')                  
assert   2.016 == molar_mass('H2')                 
assert  18.015 == molar_mass('H2O')                
assert  34.014 == molar_mass('H2O2')               
assert  34.014 == molar_mass('(HO)2')              
assert 142.036 == molar_mass('Na2SO4')             
assert  84.162 == molar_mass('C6H12')              
assert 186.295 == molar_mass('COOH(C(CH3)2)3CH3')  
assert 176.124 == molar_mass('C6H4O2(OH)4')        
assert 386.664 == molar_mass('C27H46O')            
assert 315     == molar_mass('Uue')