65. Valid Number

Problem Link

Description

---

Given a string s, return whether s is a valid number.

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".

Formally, a valid number is defined using one of the following definitions:

1. An integer number followed by an optional exponent.
2. A decimal number followed by an optional exponent.

An integer number is defined with an optional sign '-' or '+' followed by digits.

A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions:

1. Digits followed by a dot '.'.
2. Digits followed by a dot '.' followed by digits.
3. A dot '.' followed by digits.

An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number.

The digits are defined as one or more digits.

 

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 '.'.

Solution

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Python3

class Solution:
    def isNumber(self, s: str) -> bool:
        s = s.strip()
        pointSeen = eSeen = numberSeen = False
        
        for i,x in enumerate(s):
            if x >= '0' and x <= '9':
                numberSeen = True
            elif x == '.':
                if pointSeen or eSeen: return False
                pointSeen = True
            elif x == 'e' or x == 'E':
                if eSeen or not numberSeen: return False
                eSeen = True
                numberSeen = False
            elif x == '+' or x == '-':
                if i != 0 and s[i - 1] != 'e' and s[i - 1] != 'E': return False
            else:
                return False
        
        return numberSeen
 

Java

class Solution {
    public boolean isNumber(String s) {
        s = s.trim();
        boolean pointSeen = false;
        boolean eSeen = false;
        boolean numberSeen = false;
        
        for (int i=0; i<s.length(); i++) {
            if('0' <= s.charAt(i) && s.charAt(i) <= '9') {
                numberSeen = true;
            } else if(s.charAt(i) == '.') {
                if(eSeen || pointSeen)
                    return false;
                pointSeen = true;
            } else if(s.charAt(i) == 'e' || s.charAt(i) == 'E') {
                if(eSeen || !numberSeen)
                    return false;
                numberSeen = false;
                eSeen = true;
            } else if(s.charAt(i) == '-' || s.charAt(i) == '+') {
                if(i != 0 && s.charAt(i-1) != 'e' && s.charAt(i-1) != 'E')
                    return false;
            } else
                return false;
        }
        
        return numberSeen;
    }
}