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65. Valid Number

Difficulty Topics

Description

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

 

Constraints:

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

Solution

valid-number.py
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
valid-number.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;
    }
}