65-Valid-Number.md

65. Valid Number

Validate if a given string can be interpreted as a decimal number.

Some examples:

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
" -90e3 " => true
" 1e" => false
"e3" => false
" 6e-1" => true
" 99e2.5 " => false
"53.5e93" => true
" --6 " => false
"-+3" => false
"95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. It would be best if you gathered all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9
• Exponent - "e"
• Positive/negative sign - "+"/"-"
• Decimal point - "."

Of course, the context of these characters also matters in the input.

Example 1:

Input: s = "0"
Output: true

Example 2:

Input: s = "3"
Output: true

Constraints:

• 1 <= s.length <= 20
• s consists of only English letters, digits, space ' ', plus '+', minus '-', or dot '.'

Solution

class Solution:
    def isNumber(self, s: str) -> bool:
        s = s.strip()
        point = expo = digit = False
        for i in range(len(s)):
            if s[i] in ['+', '-']:
                if i > 0 and s[i-1] != 'e':
                    return False
            elif s[i] == '.':
                if point or expo:
                    return False
                point = True
            elif s[i] == 'e':
                if expo or not digit:
                    return False
                expo, digit = True, False
            elif s[i].isdigit():
                digit = True
            else:
                return False
        return digit

Theis is not difficult logic but extremely unfriendly with the conditions. Hated it. Python could do better:

class Solution:
    def isNumber(self, s: str) -> bool:
        try:
            float(s)
            return True
        except :
            return False