《算法競賽入門經典2ndEdition 》習題3-2 得分(Molar Mass, Uva1586)

用了isdigit() isalpha() 後還是比較簡單的。

#include <cstdio>
#include <cstring>
#include <cctype>

using namespace std;

const int maxn = 80;
char s[maxn + 10];

double f(char);
int main()
{     
  int t;
  scanf("%d", &t);
  while(t--)
  {
    double ans = 0;
    scanf("%s", s);
    int len = strlen(s);
    for(int i = 0; i < len; )
    {
      if(isalpha(s[i]))
      {
        double base = f(s[i]), num = 0;
        while(isdigit(s[++i]))
        {
          num *= 10;
          num += s[i] - '0';
        }
        if(num == 0) ans += base;
        else ans += base * num;
      }
    }
    printf("%.3f\n", ans);
  }
  return 0;
}

double f(char ch)
{
  const double c = 12.01, h = 1.008, o = 16.00, n = 14.01;
  switch(ch)
  {
    case 'C': return c;
    case 'H': return h;
    case 'O': return o;
    case 'N': return n;
  }
}