【luogu P4711 「化学」相对分子质量】 题解

题目链接：https://www.luogu.org/problemnew/show/P4711

要细心模拟

#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <iostream>
using namespace std;
char s[10001];
int k;
double nans1, nans2, fans, ffans, nans3, nans4;
double koushu(char a, char b)
{
    if(a == 'A')
    {
        if(b == 'g')
        return 108;
        if(b == 'u')
        return 197;
        if(b == 'l')
        return 27;
    } 
    if(a == 'H')
    {
        if(b == '#')
        return 1;
        if(b == 'g')
        return 201;
        if(b == 'f')
        return 178.5;
    }
    if(a == 'C')
    {
        if(b == '#')
        return 12;
        if(b == 'l')
        return 35.5;
        if(b == 'a')
        return 40;
        if(b == 'u')
        return 64;
    }
    if(a == 'N')
    {
        if(b == '#')
        return 14;
        if(b == 'a')
        return 23;
    }
    if(a == 'O')
    {
        if(b == '#')
        return 16;
    }
    if(a == 'F')
    {
        if(b == '#')
        return 19;
        if(b == 'e')
        return 56;
    }
    if(a == 'M')
    {
        if(b == 'g')
        return 24;  
        if(b == 'n')
        return 55;
    }
    if(a == 'S')
    {
        if(b == 'i')
        return 28;
        if(b == '#')
        return 32;
    }
    if(a == 'P')
    {
        if(b == '#')
        return 31;
        if(b == 't')
        return 195;
    }
    if(a == 'K')
    {
        if(b == '#')
        return 39; 
    }
    if(a == 'Z')
    {
        if(b == 'n')
        return 65;
    }
    if(a == 'I')
    {
        if(b == '#')
        return 127; 
    }
    if(a == 'B')
    {
        if(b == 'a')
        return 137;
    }
}
bool flag = 0;
int main()
{
    cin>>s;
    int len = strlen(s);
    for(int i = 0; i < len; i++)
    {
        if(s[i] == '~')
        {
        	if(s[i+1] > 48 && s[i+1] <= 57 && s[i+2] >= 48 && s[i+2] <= 57)
            {
            	ffans = 18*(10*(s[i+1]-'0')+s[i+2]-'0'); 
				fans += ffans;
            	break;
			}//十位数的水 
			else if(s[i+1] > 48 && s[i+1] <= 57)
			{
				ffans = 18*(s[i+1]-'0');
				fans += ffans;
            	break;
			}//个位数的水 
			else if(s[i+1] == 'H')
                        {
				ffans += 18;
           		        fans += ffans;
            	break; 
			}//一个水 
        }
		
        if(s[i] == '(') // 抠括号里的 
        {
            for(int j = i+1; s[j] != ')'; j++)
            {
                if((s[j] >= 65 && s[j] <= 90) &&(s[j+1] >= 97 && s[j+1] <= 122))
                {
                    nans3 += koushu(s[j],s[j+1]);
                    if(s[j+2] == '_')
                    nans3 = nans3*(s[j+4]-'0'); 
                    nans1 += nans3;
		    nans3 = 0;
		}
                if((s[j] >= 65 && s[j] <= 90) &&(s[j+1] <= 97 || s[j+1] >= 122))
                {
                    nans4 += koushu(s[j],'#');
                    if(s[j+1] == '_')
                    nans4 = nans4*(s[j+3]-'0');
                    nans1 += nans4;
                    nans4 = 0;
                }
                k = j;
                i = j+1;//处理完括号，把i调到下一位，否则会重复加
            }
            if(s[k+2] == '_')
            nans1 = nans1*(s[k+4]-'0');
            fans += nans1;
            nans1 = 0;
        }
        if((s[i] >= 65 && s[i] <= 90) &&(s[i+1] >= 97 && s[i+1] <= 122))
        {
            nans2 += koushu(s[i],s[i+1]);
            if(s[i+2] == '_')
            nans2 = nans2*(s[i+4]-'0');
            fans += nans2;
            nans2 = 0;
            continue;
        }

        if((s[i] >= 65 && s[i] <= 90) &&(s[i+1] <= 97 || s[i+1] >= 122))
        {
            nans2 += koushu(s[i],'#');
            if(s[i+1] == '_')
            nans2 = nans2*(s[i+3]-'0');
            fans += nans2;
            nans2 = 0;
            continue;
        }
    }
    cout<<fans;
    return 0;
}