【白书之路】 1586 - Molar mass 字符串分离处理

1586 - Molar mass

Anorganiccompound isanymemberofalargeclassofchem-

ical compounds whose molecules contain carbon. The molar

mass ofanorganiccompoundisthemassofonemoleofthe

organiccompound. Themolarmassofanorganiccompound

can be computed from the standard atomic weights of the

elements.

When an organic compound is given as a molecular for-

mula,Dr. CHONwantstoﬁnditsmolarmass. Amolecular

formula,suchasC3H4O3,identiﬁeseachconstituentelementby

itschemicalsymbolandindicatesthenumberofatomsofeach

elementfoundineachdiscretemoleculeofthatcompound. If

a molecule contains more than one atom of a particular ele-

ment,thisquantityisindicatedusingasubscriptafterthechemicalsymbol.

In this problem, we assume that the molecular formula is represented by only four elements, ‘C’

(Carbon),‘H’(Hydrogen),‘O’(Oxygen),and‘N’(Nitrogen)withoutparentheses.

Thefollowingtableshowsthatthestandardatomicweightsfor‘C’,‘H’,‘O’,and‘N’.

AtomicName

Carbon

Hydrogen

Oxygen

StandardAtomicWeight 12.01g/mol 1.008g/mol 16.00g/mol 14.01g/mol

Nitrogen

Forexample,themolarmassofamolecularformulaC6H5OHis94.108g/molwhichiscomputedby

6×(12.01g/mol)+6×(1.008g/mol)+1×(16.00g/mol).

Givenamolecularformula,writeaprogramtocomputethemolarmassoftheformula.

Input

Yourprogramistoreadfromstandardinput. TheinputconsistsofT testcases. Thenumberoftest

cases T is given in the ﬁrst line of the input. Each test case is given in a single line, which contains

a molecular formula as a string. The chemical symbol is given by a capital letter and the length of

the string is greater than 0 and less than 80. The quantity number n which is represented after the

chemicalsymbolwouldbeomittedwhenthenumberis1(2≤n≤99).

Output

Yourprogramistowritetostandardoutput. Printexactlyonelineforeachtestcase. Thelineshould

containthemolarmassofthegivenmolecularformula.

Sample Input

C6H5OH

NH2CH2COOH

C12H22O11

Sample Output

12.010

94.108

75.070

342.296

只要是上过高中，算摩尔质量神马的都是浮云，这里有两个关键：

1.如何在O(1)的时间复杂度内得到一个原子的质量

2.如何将字符串中的数字分离出来

对于第一个问题，可以使用简单的哈希处理，将字母的ASCII码与数组下标对应起来，从而可以获取单个原子的摩尔质量。

对于第二个问题，我使用边遍历边计算的方式，比如对于一个数字字符串"1234"，我们先定义一个变量num=0，此时指针p=0，首先计算num=num*10，然后计算num=num+str[i]-'0'，i++，重复这个过程，即可将整个字符串变为数字。

当然，也可以使用如atoi()或者sscanf()之类的函数进行转换。

最后，将所有的质量相加即可得到最终的摩尔质量。

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MAX 90
using namespace std;

double mass[13];
char formula[MAX];
int len;


bool is_uper(char c)//判断是否为大写字母
{
    if(c>='A'&&c<='Z')
        return true;
    else
        return false;
}
bool is_digit(char c)//判断是否为数字
{
    if(c>='0'&&c<='9')
        return true;
    else
        return false;
}

void init()//初始化
{
    mass[0]=12.01;
    mass[5]=1.008;
    mass[11]=14.01;
    mass[12]=16.00;

}
int main()
{
    init();
    int t,i,j;
    double atom_mass;//原子质量
    double molar_mass;//摩尔质量
    int quantity;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%s",formula);
        len=strlen(formula);
        molar_mass=0;
        for(i=0; i<len;)//遍历字符串
        {
            if(is_uper(formula[i]))//如果是大写字母
            {

                atom_mass=mass[formula[i]-'C'];//计算这个原子的质量
                //printf("atom mass=%lg\n",atom_mass);
                i++;
                quantity=0;
                while(is_digit(formula[i]))//数字分离
                {
                    quantity*=10;
                    quantity+=formula[i]-'0';
                    i++;
                }
                //printf("quantity=%d\n",quantity);
                if(quantity==0)
                    quantity=1;
                molar_mass+=atom_mass*quantity;//计算摩尔质量
            }
        }
        printf("%.3f\n",molar_mass);
    }
    return 0;
}

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【白书之路】 1586 - Molar mass 字符串分离处理

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