[Molar Mass, ACM/ICPC Seoul 2007, UVA1586]

主要是固定位 的思想，这是最后的代码，不过中间一直wrong answer，一直找不出，原来是15写成了14.

#include <stdio.h>
#include <string.h>

int isnum(char c) {
    return c>='0' && c<='9';
}

int main() {
    int T;
    char s[85];
    //freopen("test.txt", "r", stdin);
    double wei[15];
    wei['C'- 'A'] = 12.01;
    wei['H'- 'A'] = 1.008;
    wei['O'- 'A'] = 16.00;
    wei['N'- 'A'] = 14.01;
    scanf("%d", &T);
    while(T--) {
        scanf("%s", s);
        int len = strlen(s);
        double sum = 0;
        for(int i=0; s[i]!='\0'; ++i) {
            if(i+3 == len) {
                if(isnum(s[i+1]) && isnum(s[i+2])) {
                    sum += wei[s[i] - 'A'] * ((s[i+1] - '0')*10 + (s[i+2] - '0'));
                    break;
                }
                else if(isnum(s[i+1])) {
                    sum += wei[s[i] - 'A'];
                    i++;
                }
            }
            if(i+2 == len && isnum(s[i+1])) {
                sum += wei[s[i] - 'A'] * (s[i+1] - '0');
                break;
            }

            if(isnum(s[i+1]) && isnum(s[i+2])) {
                sum +=  wei[s[i] - 'A'] * ((s[i+1] - '0')*10 + (s[i+2] - '0'));
                i+=2;
            }
            else if(isnum(s[i+1])) {
                sum +=  wei[s[i] - 'A'] * (s[i+1] - '0');
                i++;
            }
            else {
                sum +=  wei[s[i] - 'A'];
            }
        }
        printf("%.3f\n", sum);
    }
    return 0;
}