A valid number can be split up into these components (in order):
- A decimal number or an integer.
- (Optional) An 'e' or 'E', followed by an integer.
A decimal number can be split up into these components (in order):
- (Optional) A sign character (either '+' or '-').
- One of the following formats:
- One or more digits, followed by a dot '.'.
- One or more digits, followed by a dot '.', followed by one or more digits.
- A dot '.', followed by one or more digits.
An integer can be split up into these components (in order):
- (Optional) A sign character (either '+' or '-').
- One or more digits.
For example, all the following are valid numbers: ["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"], while the following are not valid numbers: ["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"].
Given a string s, return true if s is a valid number.
Example 1:
Input: s = "0"
Output: true
Example 2:
Input: s = "e"
Output: false
Example 3:
Input: s = "."
Output: false
Constraints:
- 1 <= s.length <= 20
- s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.
class Solution {
public boolean isNumber(String s) {
if (s == null || s.trim().length() == 0) {
return false;
}
boolean seenNum = false;
boolean seenE = false;
boolean seenD = false;
s = s.trim();
for (int i=0; i < s.length(); ++i) {
char c = s.charAt(i);
switch(c) {
case '.':
if (seenD || seenE) return false;
seenD = true;
break;
case 'e':
case 'E':
if (seenE || !seenNum) return false;
seenE = true;
seenNum = false;
break;
case '+':
case '-':
if (i != 0 && s.charAt(i-1) != 'e') return false;
seenNum = false;
break;
default:
if (c - '0' < 0 || c - '0' > 9) return false;
seenNum = true;
}
}
return seenNum;
}
}