Validate if a given string is numeric.
Some examples:"0" => true" 0.1 " => true"abc" => false"1 a" => false"2e10" => true
Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.
要写对这题着实不容易，很多细节需要考虑。先看看测试用例有哪些，然后再写就比较有针对性。最后看看哪些test case错了，再修一下bug。
1 class Solution { 2 public: 3 bool isNumber(const char *s) { 4 // Start typing your C/C++ solution below 5 // DO NOT write int main() function 6 if (s == NULL) 7 return false; 8 9 while(isspace(*s)) 10 s++; 11 12 if (*s == '+' || *s == '-') 13 s++; 14 15 bool eAppear = false; 16 bool dotAppear = false; 17 bool firstPart = false; 18 bool secondPart = false; 19 bool spaceAppear = false; 20 while(*s != '\0') 21 { 22 if (*s == '.') 23 { 24 if (dotAppear || eAppear || spaceAppear) 25 return false; 26 else 27 dotAppear = true; 28 } 29 else if (*s == 'e' || *s == 'E') 30 { 31 if (eAppear || !firstPart || spaceAppear) 32 return false; 33 else 34 eAppear = true; 35 } 36 else if (isdigit(*s)) 37 { 38 if (spaceAppear) 39 return false; 40 41 if (!eAppear) 42 firstPart = true; 43 else 44 secondPart = true; 45 } 46 else if (*s == '+' || *s == '-') 47 { 48 if (sapceAppear) 49 return false; 50 51 if (!eAppear || !(*(s-1) == 'e' || *(s-1) == 'E')) 52 return false; 53 } 54 else if (isspace(*s)) 55 spaceAppear = true; 56 else 57 return false; 58 59 s++; 60 } 61 62 if (!firstPart) 63 return false; 64 else if (eAppear && !secondPart) 65 return false; 66 else 67 return true; 68 } 69 };