65. Valid Number - jiejackyzhang/leetcode-note GitHub Wiki

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.

解题思路为：

1. 首先trim并转换为char array；
2. 判断sign；
3. 判断字符是num，dot或exp，并做相应判断。

public class Solution {
    public boolean isNumber(String s) {
        if(s == null || s.length() == 0) return false;
        char[] ch = s.trim().toCharArray();
        if(ch.length == 0) return false;
        boolean num = false, dot = false, exp = false;
        int i = 0;
        if(ch[0] == '+' || ch[0] == '-') i++;
        for(; i < ch.length; i++) {
            if(Character.isDigit(ch[i])) {
                num = true;
            } else if(ch[i] == '.') {
                if(dot || exp) return false;
                dot = true;
            } else if(ch[i] == 'e') {
                if(exp || !num) return false;
                exp = true;
                num = false;
            } else if(ch[i] == '+' || ch[i] == '-') {
                if(ch[i-1] != 'e') return false;
            } else {
                return false;
            }
        }
        return num;
    }
}