g0001_0100.s0065_valid_number.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0065_valid_number;

// #Hard #String #2023_08_11_Time_1_ms_(100.00%)_Space_41.3_MB_(91.10%)

/**
 * 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 `'.'`.
**/
public class Solution {
    public boolean isNumber(String s) {
        if (s == null || s.length() == 0) {
            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;
    }
}