LeetCode-in-Java

65. Valid Number

Hard

A valid number can be split up into these components (in order):

1. A decimal number or an integer.
2. (Optional) An 'e' or 'E', followed by an integer.

A decimal number can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. One of the following formats:
   1. One or more digits, followed by a dot '.'.
   2. One or more digits, followed by a dot '.', followed by one or more digits.
   3. A dot '.', followed by one or more digits.

An integer can be split up into these components (in order):

1. (Optional) A sign character (either '+' or '-').
2. 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

Example 4:

Input: s = “.1”

Output: true

Constraints:

• 1 <= s.length <= 20
• s consists of only English letters (both uppercase and lowercase), digits (0-9), plus '+', minus '-', or dot '.'.

Solution

public class Solution {
    public boolean isNumber(String s) {
        if (s == null || s.isEmpty()) {
            return false;
        }
        boolean eSeen = false;
        boolean numberSeen = false;
        boolean decimalSeen = false;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c >= 48 && c <= 57) {
                numberSeen = true;
            } else if (c == '+' || c == '-') {
                if (i == s.length() - 1
                        || (i != 0 && s.charAt(i - 1) != 'e' && s.charAt(i - 1) != 'E')) {
                    return false;
                }
            } else if (c == '.') {
                if (eSeen || decimalSeen) {
                    return false;
                }
                decimalSeen = true;
            } else if (c == 'e' || c == 'E') {
                if (i == s.length() - 1 || eSeen || !numberSeen) {
                    return false;
                }
                eSeen = true;
            } else {
                return false;
            }
        }
        return numberSeen;
    }
}

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