Leetcode#65 Valid Number

一道考察"工程"能力的好题，但是你丫能说明一下规则不。。

用状态机求解:

当遍历完字符串后：

1. 绿色的状态至少要出现1个

2. 红色的状态不能作为终结状态

代码：

 1 enum Status {
 2   PRE_PADDING,
 3   SIGN,
 4   NUMBER_BEFORE_POINT,
 5   POINT,
 6   NUMBER_AFTER_POINT,
 7   EXPONENT,
 8   EXPONENT_SIGN,
 9   EXPONENT_NUMBER,
10   POST_PADDING
11 };
12 
13 bool isNumber(const char *s) {
14   bool mask[10] = {false};
15   Status state = PRE_PADDING;
16 
17   while (*s) {
18     switch (state) {
19     case PRE_PADDING:
20       if (*s == ' ') mask[state = PRE_PADDING] = true;
21       else if (*s == '+' || *s == '-') mask[state = SIGN] = true;
22       else if (*s >= '0' && *s <= '9') mask[state = NUMBER_BEFORE_POINT] = true;
23       else if (*s == '.') mask[state = POINT] = true;
24       else return false;
25       break;
26     case SIGN:
27       if (*s >= '0' && *s <= '9') mask[state = NUMBER_BEFORE_POINT] = true;
28       else if (*s == '.') mask[state = POINT] = true;
29       else return false;
30       break;
31     case NUMBER_BEFORE_POINT:
32       if (*s >= '0' && *s <= '9') mask[state = NUMBER_BEFORE_POINT] = true;
33       else if (*s == '.') mask[state = POINT] = true;
34       else if (*s == 'e') mask[state = EXPONENT] = true;
35       else if (*s == ' ') mask[state = POST_PADDING] = true;
36       else return false;
37       break;
38     case POINT:
39       if (*s >= '0' && *s <= '9') mask[state = NUMBER_AFTER_POINT] = true;
40       else if (*s == 'e') mask[state = EXPONENT] = true;
41       else if (*s == ' ') mask[state = POST_PADDING] = true;
42       else return false;
43       break;
44     case NUMBER_AFTER_POINT:
45       if (*s >= '0' && *s <= '9') mask[state = NUMBER_AFTER_POINT] = true;
46       else if (*s == 'e') mask[state = EXPONENT] = true;
47       else if (*s == ' ') mask[state = POST_PADDING] = true;
48       else return false;
49       break;
50     case EXPONENT:
51       if (*s >= '0' && *s <= '9') mask[state = EXPONENT_NUMBER] = true;
52       else if (*s == '+' || *s == '-') mask[state = EXPONENT_SIGN] = true;
53       else return false;
54       break;
55     case EXPONENT_SIGN:
56       if (*s >= '0' && *s <= '9') mask[state = EXPONENT_NUMBER] = true;
57       else return false;
58       break;
59     case EXPONENT_NUMBER:
60       if (*s >= '0' && *s <= '9') mask[state = EXPONENT_NUMBER] = true;
61       else if (*s == ' ') mask[state = POST_PADDING] = true;
62       else return false;
63       break;
64     case POST_PADDING:
65       if (*s == ' ') mask[state = POST_PADDING] = true;
66       else return false;
67       break;
68     default:
69       return false;
70     }
71     s++;
72   }
73 
74   return !(state == PRE_PADDING
75            || state == SIGN
76            || state == EXPONENT
77            || state == EXPONENT_SIGN)
78     && (mask[NUMBER_BEFORE_POINT]
79         || mask[NUMBER_AFTER_POINT]);
80 }

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原文地址：https://www.cnblogs.com/boring09/p/4244261.html