LeetCode – Refresh – Valid Number

 1 class Solution {
 2 public:
 3     bool isNumber(string s) {
 4         int start = 0, end = s.size()-1;
 5         if (end == -1) return false;
 6         while (start <= end && s[start] == ‘ ‘) start++;
 7         while (end >= start && s[end] == ‘ ‘) end--;
 8         bool dotflag = false, expflag = false, numflag = false;
 9         for (int i = start; i <= end; i++) {
10             if (s[i] >= ‘0‘ && s[i] <= ‘9‘) {
11                 numflag = true;
12             } else if (s[i] == ‘e‘) {
13                 if (expflag || !numflag) return false;
14                 expflag = true, numflag = false;
15             } else if (s[i] == ‘.‘) {
16                 if (dotflag || expflag) return false;
17                 dotflag = true;
18             } else if (s[i] == ‘+‘ || s[i] == ‘-‘) {
19                 if (i > start && s[i-1] != ‘e‘) return false;
20             } else return false;
21         }
22         return numflag;
23     }
24 };