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.

bool isNumber(string s) {    int l = s.length(), i;    bool flag=0, point[2]={
   0,0}, num[2]={
   0,0};    for(i=0; s[i] == ' '; i++);    for(; i

测试用例：

"0e" -- false

". 1" -- false

"-1." -- true

".-4" -- false

"+.8" -- true

"6e6.5" -- false