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

Add a new file string_is_valid_number.py in string directory

strings/string_is_valid_number.py

@@ -0,0 +1,134 @@
+"""
+Solution By: Reniz Shah
+Topic: Deterministic Finite Automaton (DFA)
+Given a string s, return whether s is a valid number or not
+Input: s = -90E3
+Output: True
+Leetcode link: https://leetcode.com/problems/valid-number/description/
+"""
+
+
+def classify_char(char):
+    """
+    Classifies a character into one of the following categories:
+
+    - 'numeric': if the character is a digit (0-9)
+    - 'ign': if the character is a plus sign (+) or a minus sign (-)
+    - 'exponent': if the character is an 'e' or 'E' (used in exponential notation)
+    - 'decimal': if the character is a decimal point (.)
+    - None: if the character does not fit into any of the above categories
+
+    Parameters:
+    char (str): The character to be classified
+
+    Returns:
+    str: The classification of the character
+
+    >>> classify_char('2')
+    'numeric'
+    >>> classify_char('-')
+    'sign'
+    >>> classify_char('e')
+    'exponent'
+    >>> classify_char('.')
+    'decimal'
+    >>> classify_char('r')
+
+    """
+
+    if char.isdigit():
+        return "numeric"
+    if char in "+-":
+        return "sign"
+    if char in "eE":
+        return "exponent"
+    if char == ".":
+        return "decimal"
+    return None
+
+
+def is_valid_number(s: 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
+    """
+
+    state_machine = {
+        "initial": {"numeric": "whole", "sign": "signed", "decimal": "fractional"},
+        "signed": {"numeric": "whole", "decimal": "fractional"},
+        "whole": {"numeric": "whole", "decimal": "Fraction", "exponent": "exponential"},
+        "fractional": {"numeric": "Fraction"},
+        "Fraction": {"numeric": "Fraction", "exponent": "exponential"},
+        "exponential": {"numeric": "Exp_number", "sign": "Exp_sign"},
+        "Exp_sign": {"numeric": "Exp_number"},
+        "Exp_number": {"numeric": "Exp_number"},
+    }
+
+    valid_final_states = {"whole", "Fraction", "Exp_number"}
+    current_state = "initial"
+
+    for char in s:
+        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()