[leetcode] Valid Number

Valid Number

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.

 

//模拟数字组成即可

 

class Solution
{
public:
  bool isNumber(const char *s)
  {
    bool has_front_num = false, has_back_num = false, has_e = false;
    int len = strlen(s);
    int i = 0;

    while(i < len && ' ' == s[i])
      i++;

    if(i == len) return false;

    if(i < len && (s[i] == '+' || s[i] == '-'))
      i++;

    while(i < len && isdigit(s[i]))
    {
      i++;
      has_front_num = true;
    }

    if(i < len && s[i] == '.')
      i++;
   
    while(i < len && isdigit(s[i]))
    {
      i++;
      has_front_num = true;
    }

    if(i < len && (s[i] == 'e' || s[i] == 'E') && has_front_num)
    {
      i++;
      has_e = true;
      if(i == len) return false;
    }

   
    if(i < len && (s[i] == '+' || s[i] == '-') && has_e)
      i++;
   
    while(i < len && isdigit(s[i]) && has_e)
    {
      i++;
      has_back_num = true;
    }

    while(i < len && s[i] == ' ')
      i++;

    if(i == len && has_e && has_back_num)
      return true;
    else if(i == len && !has_back_num && !has_e && has_front_num)
      return true;

    return false;
  }
};