LC-65

主要问题：

判断输入的字符串是否一个合法数字

思路：

垃圾题目，不说清楚格式。。只能靠试（小数点前后有没有数字真的恶心）

思路就是有限状态机，下面是我自己摸索出来的图，按着这个来打代码就行了。

代码：

 1 class Solution {
 2 public:
 3     bool isNumber(string s) {
 4         int state = 0;
 5         while(s[0]==' ')  s.erase(0,1); //删除前面的空格
 6         while(s[s.length()-1]==' ') s.erase(s.length()-1, 1); //删除最后的空格
 7         for (int i = 0; i < s.length(); i++) {
 8             char c = s[i];
 9             if (state == 0) {
10                 if (c == '+' || c == '-') state = 1;
11                 else if (c >= '0' && c <= '9') state = 2;
12                 else if (c == '.') state = 3;
13                 else return false;
14             }
15             else if (state == 1) {
16                 if (c >= '0' && c <= '9') state = 2;
17                 else if (c == '.') state = 3;
18                 else return false;
19             }
20             else if (state == 2) {
21                 if (c >= '0' && c <= '9') state = 2;
22                 else if (c == '.') state = 4;
23                 else if (c == 'e') state = 5;
24                 else return false;
25             }
26             else if (state == 3) {
27                 if (c >= '0' && c <= '9') state = 4;
28                 else return false;
29             }
30             else if (state == 4) {
31                 if (c >= '0' && c <= '9') state = 4;
32                 else if (c == 'e') state = 5;
33                 else return false;
34             }
35             else if (state == 5) {
36                 if (c == '+' || c == '-') state = 6;
37                 else if (c >= '0' && c <= '9') state = 7;
38                 else return false;
39             }
40             else if (state == 6) {
41                 if (c >= '0' && c <= '9') state = 7;
42                 else return false;
43             }
44             else if (state == 7) {
45                 if (c >= '0' && c <= '9') state = 7;
46                 else return false;
47             }
48         }
49         return (state == 2 || state == 4 || state == 7);
50     }
51 };