65. Valid Number - cocoder39/coco39_LC GitHub Wiki

65. Valid Number

2nd revision

• sign: has to be leading eg 6+1 is invalid
• int: 0 or 1 leading sign, followed by digits, no decimal
  • once a sign is found, no more sign
  • if it is int (eg following exp), there is no decimal
  • no digit is invalid eg .
• decimal: 0 or 1 leading sign
  • definition
    • decimal + digit eg .4
    • digit + decimal eg 3.
    • digit + decimal + digit 3.4
  • violation
    • once a sign is found, no more sign
    • once a decimal is found, no more decimal
    • no digit is invalid
• exp: e/E followed by int
  • there should be digit before and after e/E, eg e is invalid
  • once e/E is found, no more e eg 3e4e is invalid
• any char that is not digit, sign, e/E, decimal, then it is invalid
• valid number: int or decimal followed by 0 or 1 exp

class Solution:
    def isNumber(self, s: str) -> bool:
        canHaveSign = True
        canHaveDecimalPoint = True
        canHaveExp = True
        hasDigit = False
        for ch in s:
            if ch in '+-':
                if not canHaveSign:
                    return False
                canHaveSign = False
            elif ch in 'Ee':
                if not canHaveExp or not hasDigit:
                    return False
                canHaveSign = True
                canHaveDecimalPoint = False
                canHaveExp = False
                hasDigit = False
            elif ch == '.':
                if not canHaveDecimalPoint:
                    return False
                canHaveSign = False
                canHaveDecimalPoint = False
            elif ch.isdigit():
                canHaveSign = False
                hasDigit = True
            else:
                return False
        return hasDigit

class Solution:
    def isNumber(self, s: str) -> bool:
        seen_digit = seen_exp = seen_dot = False
        for i, ch in enumerate(s):
            if ch.isdigit():
                seen_digit = True
            elif ch in '+-':
                if i > 0 and s[i-1] not in 'eE':
                    return False
            elif ch in 'eE':
                if seen_exp or not seen_digit:
                    return False
                seen_exp = True
                seen_digit = False
            elif ch == '.':
                if seen_dot or seen_exp:
                    return False
                seen_dot = True
            else:
                return False
        
        return seen_digit