# Check 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.

## Solution

This finite-state machine solution.

## Code

``````public class Solution {
public boolean isNumber(String s) {
int start = 0, end = s.length() -1;
boolean dot = false, exp = false, digit = false;
while (start <= end && (s.charAt(start) == ' ')) ++start;
while (start <= end && (s.charAt(end) == ' ')) --end;
if (start <= end && (s.charAt(start) == '+' || s.charAt(start) == '-')) ++start;
if (start > end) return false;
for ( ; start <= end; ++start) {
if (Character.isDigit(s.charAt(start))) digit = true;
else if (s.charAt(start) == 'e' || s.charAt(start) == 'E') {
if (exp == true || digit == false || start == end) return false;
exp = true;
} else if (s.charAt(start) == '.') {
if (dot == true || exp == true) return false;
if (digit == false && start == end) return false;
dot = true;
} else if (s.charAt(start) == '+' || s.charAt(start) == '-') {
if (start == end) return false;
if (s.charAt(start-1) != 'e' && s.charAt(start-1) != 'E') return false;
} else return false;
}
return true;
}
}
``````