Solution.java

package g0001_0100.s0065_valid_number;

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

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;
    }
}