标签：code init close 正则 inf only name event fail
题目描述：
方法一：逻辑判断法：O(N)
class Solution: def isNumber(self, s: str) -> bool: s = s.strip() met_dot = met_e = met_digit = False for i, char in enumerate(s): if char in (‘+‘, ‘-‘): if i > 0 and s[i-1] != ‘e‘ and s[i-1] != ‘E‘: return False elif char == ‘.‘: if met_dot or met_e: return False met_dot = True elif char == ‘e‘ or char == ‘E‘: if met_e or not met_digit: return False met_e, met_digit = True, False # e后必须接，所以这时重置met_digit为False,以免e为最后一个char elif char.isdigit(): met_digit = True else: return False return met_digit
方法二;正则表达式
class Solution: def isNumber(self, s: str) -> bool: p = re.compile(r‘^[+-]?(\.\d+|\d+\.?\d*)([eE][+-]?\d+)?$‘) return bool(p.match(s.strip()))
方法三：try/except法
class Solution: def isNumber(self, s: str) -> bool: try: float(s) return True except: return False
方法四：确定性有限自动机
class Solution(object): def isNumber(self, s): """ :type s: str :rtype: bool """ #define DFA state transition tables states = [{}, # State (1) - initial state (scan ahead thru blanks) {‘blank‘: 1, ‘sign‘: 2, ‘digit‘:3, ‘.‘:4}, # State (2) - found sign (expect digit/dot) {‘digit‘:3, ‘.‘:4}, # State (3) - digit consumer (loop until non-digit) {‘digit‘:3, ‘.‘:5, ‘e‘:6, ‘blank‘:9}, # State (4) - found dot (only a digit is valid) {‘digit‘:5}, # State (5) - after dot (expect digits, e, or end of valid input) {‘digit‘:5, ‘e‘:6, ‘blank‘:9}, # State (6) - found ‘e‘ (only a sign or digit valid) {‘sign‘:7, ‘digit‘:8}, # State (7) - sign after ‘e‘ (only digit) {‘digit‘:8}, # State (8) - digit after ‘e‘ (expect digits or end of valid input) {‘digit‘:8, ‘blank‘:9}, # State (9) - Terminal state (fail if non-blank found) {‘blank‘:9}] currentState = 1 for c in s: # If char c is of a known class set it to the class name if c in ‘0123456789‘: c = ‘digit‘ elif c in ‘ \t\n‘: c = ‘blank‘ elif c in ‘+-‘: c = ‘sign‘ # If char/class is not in our state transition table it is invalid input if c not in states[currentState]: return False # State transition currentState = states[currentState][c] # The only valid terminal states are end on digit, after dot, digit after e, or white space after valid input if currentState not in [3,5,8,9]: return False return True
标签：code init close 正则 inf only name event fail
原文地址：https://www.cnblogs.com/oldby/p/12701580.html
