Question:

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.

Thinking:

  • Method:
    • 这道题是参考别人的答案才写出来的，用的方法是正则表达式匹配。
import java.util.regex.Matcher;
import java.util.regex.Pattern;

class Solution {
    public boolean isNumber(String s) {
        s = s.trim();
        if(s.equals("")) return false;
        Pattern p = Pattern.compile("^[+-]?((\\d+(\\.\\d*)?)|(\\.\\d+))([eE][+-]?\\d+)?");
        Matcher m = p.matcher(s);
        return m.matches();
    }
}