Valid Number--LeetCode

 1 class Solution {
 2 public:
 3 bool isNumber(string s) {
 4     if(s == " ") return false;
 5     int i = 0;
 6     int j = s.size()-1;
 7     while(s[i] == ‘ ‘) ++i;
 8     while(s[j] == ‘ ‘) --j;
 9     ++j;
10 
11     if(s[i] == ‘+‘ || s[i] == ‘-‘) ++i;
12 
13     if(i == j) return false;
14 
15     bool numberic = true;
16     bool flag = false;
17 
18     int k = scanDigits(s,i,j);
19     if (k != i)
20     {
21         flag = true;
22     }
23 
24     i = k;
25 
26     if(i < j){
27         if(s[i] == ‘.‘){
28             ++i;
29             if(i == j && !flag) return false;
30             else
31             {
32                 k = scanDigits(s,i,j);
33                 if (k != i)
34                 {
35                     flag = true;
36                 }
37                 i = k;
38                 if(i < j && (s[i] == ‘E‘||s[i] == ‘e‘))
39                     numberic = flag && isExponential(s, (++i),j);
40             }
41 
42         }
43         else if(i < j && (s[i] == ‘E‘||s[i] == ‘e‘))
44             numberic = flag && isExponential(s, ++i,j);
45         else numberic = false;
46     }
47 
48     return numberic && i == j;
49 
50 }
51 
52 int scanDigits(string str, int i,int j){
53     while(i < j && str[i] >= ‘0‘&& str[i] <= ‘9‘) ++i;
54     return i;
55 }
56 
57 bool isExponential(string str, int& i, int j){
58     if(i == j) return false;
59     if(str[i] == ‘+‘ || str[i] == ‘-‘) ++i;
60 
61     if(i == j) return false;
62     i = scanDigits(str,i,j);
63     return i==j?true:false;
64 }
65 };