ValidNumber.java

package by.andd3dfx.numeric;

/**
 * <pre>
 * <a href="https://leetcode.com/problems/valid-number/description/">Task description</a>
 *
 * 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.
 * </pre>
 *
 * @see <a href="https://youtu.be/Xy0iJ7w_UO8">Video solution</a>
 */
public class ValidNumber {

    public static boolean isNumber(String s) {
        return s.matches("[+-]?(\\d+\\.?|\\d*\\.\\d+)([eE][+-]?\\d+)?");
    }
}