目录

三个月算法进阶--day56

2020-10-18 约 262 字预计阅读 1 分钟次阅读

目录

有限状态自动机

初始状态、接受状态、状态集合、转移规则

自动机驱动的编程

暴力枚举的延伸

KMP算法

记录

leetcode剑指offer第20题表示数值的字符串

from enum import Enum

class Solution:
    def isNumber(self, s: str) -> bool:
        State = Enum("State", [
            "STATE_INITIAL",
            "STATE_INT_SIGN",
            "STATE_INTEGER",
            "STATE_POINT",
            "STATE_POINT_WITHOUT_INT",
            "STATE_FRACTION",
            "STATE_EXP",
            "STATE_EXP_SIGN",
            "STATE_EXP_NUMBER",
            "STATE_END",
        ])
        Chartype = Enum("Chartype", [
            "CHAR_NUMBER",
            "CHAR_EXP",
            "CHAR_POINT",
            "CHAR_SIGN",
            "CHAR_SPACE",
            "CHAR_ILLEGAL",
        ])

        def toChartype(ch: str) -> Chartype:
            if ch.isdigit():
                return Chartype.CHAR_NUMBER
            elif ch.lower() == "e":
                return Chartype.CHAR_EXP
            elif ch == ".":
                return Chartype.CHAR_POINT
            elif ch == "+" or ch == "-":
                return Chartype.CHAR_SIGN
            elif ch == " ":
                return Chartype.CHAR_SPACE
            else:
                return Chartype.CHAR_ILLEGAL
        
        transfer = {
            State.STATE_INITIAL: {
                Chartype.CHAR_SPACE: State.STATE_INITIAL,
                Chartype.CHAR_NUMBER: State.STATE_INTEGER,
                Chartype.CHAR_POINT: State.STATE_POINT_WITHOUT_INT,
                Chartype.CHAR_SIGN: State.STATE_INT_SIGN,
            },
            State.STATE_INT_SIGN: {
                Chartype.CHAR_NUMBER: State.STATE_INTEGER,
                Chartype.CHAR_POINT: State.STATE_POINT_WITHOUT_INT,
            },
            State.STATE_INTEGER: {
                Chartype.CHAR_NUMBER: State.STATE_INTEGER,
                Chartype.CHAR_EXP: State.STATE_EXP,
                Chartype.CHAR_POINT: State.STATE_POINT,
                Chartype.CHAR_SPACE: State.STATE_END,
            },
            State.STATE_POINT: {
                Chartype.CHAR_NUMBER: State.STATE_FRACTION,
                Chartype.CHAR_EXP: State.STATE_EXP,
                Chartype.CHAR_SPACE: State.STATE_END,
            },
            State.STATE_POINT_WITHOUT_INT: {
                Chartype.CHAR_NUMBER: State.STATE_FRACTION,
            },
            State.STATE_FRACTION: {
                Chartype.CHAR_NUMBER: State.STATE_FRACTION,
                Chartype.CHAR_EXP: State.STATE_EXP,
                Chartype.CHAR_SPACE: State.STATE_END,
            },
            State.STATE_EXP: {
                Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER,
                Chartype.CHAR_SIGN: State.STATE_EXP_SIGN,
            },
            State.STATE_EXP_SIGN: {
                Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER,
            },
            State.STATE_EXP_NUMBER: {
                Chartype.CHAR_NUMBER: State.STATE_EXP_NUMBER,
                Chartype.CHAR_SPACE: State.STATE_END,
            },
            State.STATE_END: {
                Chartype.CHAR_SPACE: State.STATE_END,
            },
        }

        st = State.STATE_INITIAL
        for ch in s:
            typ = toChartype(ch)
            if typ not in transfer[st]:
                return False
            st = transfer[st][typ]
        
        return st in [State.STATE_INTEGER, State.STATE_POINT, State.STATE_FRACTION, State.STATE_EXP_NUMBER, State.STATE_END]