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135 lines
3.4 KiB
Python
135 lines
3.4 KiB
Python
"""
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Solution By: Reniz Shah
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Topic: Deterministic Finite Automaton (DFA)
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Given a string s, return whether s is a valid number or not
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Input: s = -90E3
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Output: True
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Leetcode link: https://leetcode.com/problems/valid-number/description/
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"""
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def classify_char(char):
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"""
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Classifies a character into one of the following categories:
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- 'numeric': if the character is a digit (0-9)
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- 'ign': if the character is a plus sign (+) or a minus sign (-)
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- 'exponent': if the character is an 'e' or 'E' (used in exponential notation)
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- 'decimal': if the character is a decimal point (.)
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- None: if the character does not fit into any of the above categories
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Parameters:
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char (str): The character to be classified
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Returns:
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str: The classification of the character
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>>> classify_char('2')
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'numeric'
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>>> classify_char('-')
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'sign'
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>>> classify_char('e')
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'exponent'
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>>> classify_char('.')
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'decimal'
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>>> classify_char('r')
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"""
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if char.isdigit():
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return "numeric"
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if char in "+-":
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return "sign"
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if char in "eE":
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return "exponent"
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if char == ".":
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return "decimal"
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return None
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def is_valid_number(s: str) -> bool:
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"""
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This function checks if the input string represents a valid number.
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It uses a finite state machine to parse the input string,
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transitioning between states based on the character type.
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The function returns True if the input string represents a valid number,
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and False otherwise.
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A valid number is defined as a string that can be parsed into an
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integer, decimal, or exponent.
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>>> is_valid_number("2")
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True
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>>> is_valid_number("0089")
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True
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>>> is_valid_number("-0.1")
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True
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>>> is_valid_number("+3.14")
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True
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>>> is_valid_number("4.")
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True
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>>> is_valid_number("-.9")
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True
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>>> is_valid_number("2e10")
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True
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>>> is_valid_number("-90E3")
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True
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>>> is_valid_number("3e+7")
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True
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>>> is_valid_number("+6e-1")
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True
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>>> is_valid_number("53.5e93")
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True
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>>> is_valid_number("-123.456e789")
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True
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>>> is_valid_number("abc")
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False
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>>> is_valid_number("1a")
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False
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>>> is_valid_number("1e")
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False
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>>> is_valid_number("e3")
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False
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>>> is_valid_number("99e2.5")
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False
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>>> is_valid_number("--6")
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False
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>>> is_valid_number("-+3")
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False
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>>> is_valid_number("95a54e53")
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False
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>>> is_valid_number(".")
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False
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"""
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state_machine = {
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"initial": {"numeric": "whole", "sign": "signed", "decimal": "fractional"},
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"signed": {"numeric": "whole", "decimal": "fractional"},
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"whole": {"numeric": "whole", "decimal": "Fraction", "exponent": "exponential"},
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"fractional": {"numeric": "Fraction"},
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"Fraction": {"numeric": "Fraction", "exponent": "exponential"},
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"exponential": {"numeric": "Exp_number", "sign": "Exp_sign"},
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"Exp_sign": {"numeric": "Exp_number"},
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"Exp_number": {"numeric": "Exp_number"},
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}
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valid_final_states = {"whole", "Fraction", "Exp_number"}
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current_state = "initial"
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for char in s:
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char_type = classify_char(char)
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if char_type is None or char_type not in state_machine[current_state]:
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return False
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current_state = state_machine[current_state][char_type]
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return current_state in valid_final_states
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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