65. Valid Number.md

65. Valid Number

Validate if a given string can be interpreted as a decimal number.

Some examples:

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
" -90e3   " => true
" 1e" => false
"e3" => false
" 6e-1" => true
" 99e2.5 " => false
"53.5e93" => true
" --6 " => false
"-+3" => false
"95a54e53" => false

Note:

It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9
• Exponent - "e"
• Positive/negative sign - "+"/"-"
• Decimal point - "."
• Of course, the context of these characters also matters in the input.

Update (2015-02-10):

The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

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Solution

• mine

  • Java

    Error Answer, 1477 / 1481 test cases passed. ???

    public boolean isNumber(String s) {
        try{
            Double.parseDouble(s);
            return true;
        }catch(Exception e){
            return false;
        }
    }
    

• the most votes

  Runtime: 2 ms, faster than 90.91%,Memory Usage: 39.6 MB, less than 6.25% of Java online submissions

  public boolean isNumber(String s) {
      s = s.trim();
  
      boolean pointSeen = false;
      boolean eSeen = false;
      boolean numberSeen = false;
      boolean numberAfterE = true;
      for(int i=0; i<s.length(); i++) {
          if('0' <= s.charAt(i) && s.charAt(i) <= '9') {
              numberSeen = true;
              numberAfterE = true;
          } else if(s.charAt(i) == '.') {
              if(eSeen || pointSeen) {
                  return false;
              }
              pointSeen = true;
          } else if(s.charAt(i) == 'e') {
              if(eSeen || !numberSeen) {
                  return false;
              }
              numberAfterE = false;
              eSeen = true;
          } else if(s.charAt(i) == '-' || s.charAt(i) == '+') {
              if(i != 0 && s.charAt(i-1) != 'e') {
                  return false;
              }
          } else {
              return false;
          }
      }
  
      return numberSeen && numberAfterE;
  }