add algorithm to check if given string is valid number or not

strings/string_is_valid_number.py

@@ -0,0 +1,170 @@
+"""
+Solution By: Reniz Shah
+Topic: Deterministic Finite Automaton (DFA)
+Given a string s, return whether s is a valid number or not
+Leetcode link: https://leetcode.com/problems/valid-number/description/
+"""
+
+from enum import Enum
+
+
+class CharType(Enum):
+    NUMERIC = "NUMERIC"
+    SIGN = "SIGN"
+    EXPONENT = "EXPONENT"
+    DECIMAL = "DECIMAL"
+
+
+class State(Enum):
+    INITIAL = "INITIAL"
+    SIGNED = "SIGNED"
+    WHOLE = "WHOLE"
+    FRACTIONAL = "FRACTIONAL"
+    FRACTION = "FRACTION"
+    EXPONENTIAL = "EXPONENTIAL"
+    EXP_SIGN = "EXP_SIGN"
+    EXP_NUMBER = "EXP_NUMBER"
+
+
+state_machine: dict[State, dict[CharType, State]] = {
+    State.INITIAL: {
+        CharType.NUMERIC: State.WHOLE,
+        CharType.SIGN: State.SIGNED,
+        CharType.DECIMAL: State.FRACTIONAL,
+    },
+    State.SIGNED: {CharType.NUMERIC: State.WHOLE, CharType.DECIMAL: State.FRACTIONAL},
+    State.WHOLE: {
+        CharType.NUMERIC: State.WHOLE,
+        CharType.DECIMAL: State.FRACTION,
+        CharType.EXPONENT: State.EXPONENTIAL,
+    },
+    State.FRACTIONAL: {CharType.NUMERIC: State.FRACTION},
+    State.FRACTION: {
+        CharType.NUMERIC: State.FRACTION,
+        CharType.EXPONENT: State.EXPONENTIAL,
+    },
+    State.EXPONENTIAL: {
+        CharType.NUMERIC: State.EXP_NUMBER,
+        CharType.SIGN: State.EXP_SIGN,
+    },
+    State.EXP_SIGN: {CharType.NUMERIC: State.EXP_NUMBER},
+    State.EXP_NUMBER: {CharType.NUMERIC: State.EXP_NUMBER},
+}
+
+
+def classify_char(char: str) -> CharType | None:
+    """
+    Classifies a character into one of the following categories:
+
+    - 'CharType.NUMERIC': if the character is a digit (0-9)
+    - 'CharType.SIGN': if the character is a plus sign (+) or a minus sign (-)
+    - 'CharType.EXPONENT': if the character is an 'e' or 'E'
+        (used in exponential notation)
+    - 'CharType.DECIMAL': if the character is a decimal point (.)
+    - None: if the character does not fit into any of the above categories
+    - None: if size of char is not 1
+
+    Parameters:
+    char (str): The character to be classified
+
+    Returns:
+    CharType: The classification of the character
+
+    >>> classify_char('2')
+    <CharType.NUMERIC: 'NUMERIC'>
+    >>> classify_char('-')
+    <CharType.SIGN: 'SIGN'>
+    >>> classify_char('e')
+    <CharType.EXPONENT: 'EXPONENT'>
+    >>> classify_char('.')
+    <CharType.DECIMAL: 'DECIMAL'>
+    >>> classify_char('')
+
+    >>> classify_char('0')
+    <CharType.NUMERIC: 'NUMERIC'>
+    >>> classify_char('01')
+    """
+    if len(char) != 1:
+        return None
+    if char.isdigit():
+        return CharType.NUMERIC
+    if char in "+-":
+        return CharType.SIGN
+    if char in "eE":
+        return CharType.EXPONENT
+    if char == ".":
+        return CharType.DECIMAL
+    return None
+
+
+def is_valid_number(number_string: str) -> bool:
+    """
+    This function checks if the input string represents a valid number.
+    It uses a finite state machine to parse the input string,
+    transitioning between states based on the character type.
+    The function returns True if the input string represents a valid number,
+    and False otherwise.
+    A valid number is defined as a string that can be parsed into an
+    integer, decimal, or exponent.
+    >>> is_valid_number("2")
+    True
+    >>> is_valid_number("0089")
+    True
+    >>> is_valid_number("-0.1")
+    True
+    >>> is_valid_number("+3.14")
+    True
+    >>> is_valid_number("4.")
+    True
+    >>> is_valid_number("-.9")
+    True
+    >>> is_valid_number("2e10")
+    True
+    >>> is_valid_number("-90E3")
+    True
+    >>> is_valid_number("3e+7")
+    True
+    >>> is_valid_number("+6e-1")
+    True
+    >>> is_valid_number("53.5e93")
+    True
+    >>> is_valid_number("-123.456e789")
+    True
+
+
+    >>> is_valid_number("abc")
+    False
+    >>> is_valid_number("1a")
+    False
+    >>> is_valid_number("1e")
+    False
+    >>> is_valid_number("e3")
+    False
+    >>> is_valid_number("99e2.5")
+    False
+    >>> is_valid_number("--6")
+    False
+    >>> is_valid_number("-+3")
+    False
+    >>> is_valid_number("95a54e53")
+    False
+    >>> is_valid_number(".")
+    False
+    """
+
+    valid_final_states = {State.WHOLE, State.FRACTION, State.EXP_NUMBER}
+    current_state = State.INITIAL
+
+    for char in number_string:
+        char_type = classify_char(char)
+        if char_type is None or char_type not in state_machine[current_state]:
+            return False
+        current_state = state_machine[current_state][char_type]
+
+    return current_state in valid_final_states
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()