Task: Chemical calculator




Go: package main

import (
    "fmt"
    "strconv"
    "strings"
)

var atomicMass = map[string]float64{
    "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,
}

func replaceParens(s string) string {
    var letter byte = 'a'
    for {
        start := strings.IndexByte(s, '(')
        if start == -1 {
            break
        }
    restart:
        for i := start + 1; i < len(s); i++ {
            if s[i] == ')' {
                expr := s[start+1 : i]
                symbol := fmt.Sprintf("@%c", letter)
                s = strings.Replace(s, s[start:i+1], symbol, 1)
                atomicMass[symbol] = evaluate(expr)
                letter++
                break
            }
            if s[i] == '(' {
                start = i
                goto restart
            }
        }
    }
    return s
}

func evaluate(s string) float64 {
    s += string('[') 
    var symbol, number string
    sum := 0.0
    for i := 0; i < len(s); i++ {
        c := s[i]
        switch {
        case c >= '@' && c <= '[': 
            n := 1
            if number != "" {
                n, _ = strconv.Atoi(number)
            }
            if symbol != "" {
                sum += atomicMass[symbol] * float64(n)
            }
            if c == '[' {
                break
            }
            symbol = string(c)
            number = ""
        case c >= 'a' && c <= 'z':
            symbol += string(c)
        case c >= '0' && c <= '9':
            number += string(c)
        default:
            panic(fmt.Sprintf("Unexpected symbol %c in molecule", c))
        }
    }
    return sum
}

func main() {
    molecules := []string{
        "H", "H2", "H2O", "H2O2", "(HO)2", "Na2SO4", "C6H12", "COOH(C(CH3)2)3CH3",
        "C6H4O2(OH)4", "C27H46O", "Uue",
    }
    for _, molecule := range molecules {
        mass := evaluate(replaceParens(molecule))
        fmt.Printf("%17s -> %7.3f\n", molecule, mass)
    }
}