[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;}