65. 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.

思路：一种一种考虑

public class Solution {
    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;
    }
}