算法leetcode｜65. 有效数字（rust重拳出击）-Toy模板网

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65. 有效数字：

有效数字（按顺序）可以分成以下几个部分：

一个小数或者整数
（可选）一个 'e' 或 'E' ，后面跟着一个整数

小数（按顺序）可以分成以下几个部分：

（可选）一个符号字符（'+' 或 '-'）
下述格式之一：
1. 至少一位数字，后面跟着一个点 '.'
2. 至少一位数字，后面跟着一个点 '.' ，后面再跟着至少一位数字
3. 一个点 '.' ，后面跟着至少一位数字

整数（按顺序）可以分成以下几个部分：

（可选）一个符号字符（'+' 或 '-'）
至少一位数字

部分有效数字列举如下：["2", "0089", "-0.1", "+3.14", "4.", "-.9", "2e10", "-90E3", "3e+7", "+6e-1", "53.5e93", "-123.456e789"]

部分无效数字列举如下：["abc", "1a", "1e", "e3", "99e2.5", "--6", "-+3", "95a54e53"]

给你一个字符串 s ，如果 s 是一个 有效数字 ，请返回 true 。

样例 1：

输入：
	
	s = "0"
	
输出：
	
	true

样例 2：

输入：
	
	s = "e"
	
输出：
	
	false

样例 3：

输入：
	
	s = "."
	
输出：
	
	false

提示：

1 <= s.length <= 20
s 仅含英文字母（大写和小写），数字（0-9），加号 '+' ，减号 '-' ，或者点 '.' 。

分析：

面对这道算法题目，二当家的再次陷入了沉思。
二当家的觉得这道题和其他算法题不太一样，感觉这种判断是否有效的不太像算法。
平时看到数字大脑是瞬间判断的。
没想到写起程序却这么繁琐。
在设计模式中有一种叫做状态模式，在这里可以借鉴。
如果用一大堆分支逻辑判断，人是要疯掉的，但是用状态切换的方式，就非常的清晰。
有效数字的状态是可预知而且有限的，有限状态机，对，就是叫这个。

算法leetcode｜65. 有效数字（rust重拳出击）,LeetCode力扣算法题目,rust,golang,数据结构,算法,后端

题解：

rust：

impl Solution {
    pub fn is_number(s: String) -> bool {
        s.chars()
         .try_fold(State::new(), State::handle)
         .as_ref()
         .map_or(false, State::is_valid)
    }
}

type Result = std::result::Result<State, ()>;

enum State {
    Start,
    Sign,
    Integer,
    Dot,
    EmptyDot,
    Decimal,
    E,
    ExpSign,
    Exponent,
    End,
}

impl State {
    pub fn new() -> Self {
        State::Start
    }

    pub fn is_valid(&self) -> bool {
        use State::*;
        match self {
            Start | Sign | E | ExpSign | EmptyDot => false,
            _ => true,
        }
    }

    pub fn handle(self, c: char) -> Result {
        use State::*;
        match self {
            Start => match c {
                ' ' => Ok(Start),
                '+' | '-' => Ok(Sign),
                '0'..='9' => Ok(Integer),
                '.' => Ok(EmptyDot),
                _ => Err(()),
            }
            Sign => match c {
                '0'..='9' => Ok(Integer),
                '.' => Ok(EmptyDot),
                _ => Err(()),
            }
            Integer => match c {
                '0'..='9' => Ok(Integer),
                '.' => Ok(Dot),
                'e' | 'E' => Ok(E),
                ' ' => Ok(End),
                _ => Err(()),
            }
            EmptyDot => match c {
                '0'..='9' => Ok(Decimal), // "  .1" or "  +.1"
                _ => Err(()),
            }
            Dot => match c {
                '0'..='9' => Ok(Decimal),
                'e' | 'E' => Ok(E),   // "46.e3"
                ' ' => Ok(End),
                _ => Err(()),
            }
            Decimal => match c {
                '0'..='9' => Ok(Decimal),
                'e' | 'E' => Ok(E),
                ' ' => Ok(End),
                _ => Err(()),
            }
            E => match c {
                '+' | '-' => Ok(ExpSign),
                '0'..='9' => Ok(Exponent),
                _ => Err(()),
            }
            ExpSign => match c {
                '0'..='9' => Ok(Exponent),
                _ => Err(()),
            }
            Exponent => match c {
                '0'..='9' => Ok(Exponent),
                ' ' => Ok(End),
                _ => Err(()),
            }
            End => match c {
                ' ' => Ok(End),
                _ => Err(()),
            }
        }
    }
}

go：

type State int
type CharType int

const (
    STATE_INITIAL State = iota
    STATE_INT_SIGN
    STATE_INTEGER
    STATE_POINT
    STATE_POINT_WITHOUT_INT
    STATE_FRACTION
    STATE_EXP
    STATE_EXP_SIGN
    STATE_EXP_NUMBER
    STATE_END
)

const (
    CHAR_NUMBER CharType = iota
    CHAR_EXP
    CHAR_POINT
    CHAR_SIGN
    CHAR_ILLEGAL
)

func toCharType(ch byte) CharType {
    switch ch {
    case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
        return CHAR_NUMBER
    case 'e', 'E':
        return CHAR_EXP
    case '.':
        return CHAR_POINT
    case '+', '-':
        return CHAR_SIGN
    default:
        return CHAR_ILLEGAL
    }
}

func isNumber(s string) bool {
    transfer := map[State]map[CharType]State{
        STATE_INITIAL: map[CharType]State{
            CHAR_NUMBER: STATE_INTEGER,
            CHAR_POINT:  STATE_POINT_WITHOUT_INT,
            CHAR_SIGN:   STATE_INT_SIGN,
        },
        STATE_INT_SIGN: map[CharType]State{
            CHAR_NUMBER: STATE_INTEGER,
            CHAR_POINT:  STATE_POINT_WITHOUT_INT,
        },
        STATE_INTEGER: map[CharType]State{
            CHAR_NUMBER: STATE_INTEGER,
            CHAR_EXP:    STATE_EXP,
            CHAR_POINT:  STATE_POINT,
        },
        STATE_POINT: map[CharType]State{
            CHAR_NUMBER: STATE_FRACTION,
            CHAR_EXP:    STATE_EXP,
        },
        STATE_POINT_WITHOUT_INT: map[CharType]State{
            CHAR_NUMBER: STATE_FRACTION,
        },
        STATE_FRACTION: map[CharType]State{
            CHAR_NUMBER: STATE_FRACTION,
            CHAR_EXP:    STATE_EXP,
        },
        STATE_EXP: map[CharType]State{
            CHAR_NUMBER: STATE_EXP_NUMBER,
            CHAR_SIGN:   STATE_EXP_SIGN,
        },
        STATE_EXP_SIGN: map[CharType]State{
            CHAR_NUMBER: STATE_EXP_NUMBER,
        },
        STATE_EXP_NUMBER: map[CharType]State{
            CHAR_NUMBER: STATE_EXP_NUMBER,
        },
    }
    state := STATE_INITIAL
    for i := 0; i < len(s); i++ {
        typ := toCharType(s[i])
        if _, ok := transfer[state][typ]; !ok {
            return false
        } else {
            state = transfer[state][typ]
        }
    }
    return state == STATE_INTEGER || state == STATE_POINT || state == STATE_FRACTION || state == STATE_EXP_NUMBER || state == STATE_END
}

c++：

class Solution {
public:
    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
    };

    enum CharType {
        CHAR_NUMBER,
        CHAR_EXP,
        CHAR_POINT,
        CHAR_SIGN,
        CHAR_ILLEGAL
    };

    CharType toCharType(char ch) {
        if (ch >= '0' && ch <= '9') {
            return CHAR_NUMBER;
        } else if (ch == 'e' || ch == 'E') {
            return CHAR_EXP;
        } else if (ch == '.') {
            return CHAR_POINT;
        } else if (ch == '+' || ch == '-') {
            return CHAR_SIGN;
        } else {
            return CHAR_ILLEGAL;
        }
    }

    bool isNumber(string s) {
        unordered_map<State, unordered_map<CharType, State>> transfer{
            {
                STATE_INITIAL, {
                    {CHAR_NUMBER, STATE_INTEGER},
                    {CHAR_POINT, STATE_POINT_WITHOUT_INT},
                    {CHAR_SIGN, STATE_INT_SIGN}
                }
            }, {
                STATE_INT_SIGN, {
                    {CHAR_NUMBER, STATE_INTEGER},
                    {CHAR_POINT, STATE_POINT_WITHOUT_INT}
                }
            }, {
                STATE_INTEGER, {
                    {CHAR_NUMBER, STATE_INTEGER},
                    {CHAR_EXP, STATE_EXP},
                    {CHAR_POINT, STATE_POINT}
                }
            }, {
                STATE_POINT, {
                    {CHAR_NUMBER, STATE_FRACTION},
                    {CHAR_EXP, STATE_EXP}
                }
            }, {
                STATE_POINT_WITHOUT_INT, {
                    {CHAR_NUMBER, STATE_FRACTION}
                }
            }, {
                STATE_FRACTION,
                {
                    {CHAR_NUMBER, STATE_FRACTION},
                    {CHAR_EXP, STATE_EXP}
                }
            }, {
                STATE_EXP,
                {
                    {CHAR_NUMBER, STATE_EXP_NUMBER},
                    {CHAR_SIGN, STATE_EXP_SIGN}
                }
            }, {
                STATE_EXP_SIGN, {
                    {CHAR_NUMBER, STATE_EXP_NUMBER}
                }
            }, {
                STATE_EXP_NUMBER, {
                    {CHAR_NUMBER, STATE_EXP_NUMBER}
                }
            }
        };

        int len = s.length();
        State st = STATE_INITIAL;

        for (int i = 0; i < len; i++) {
            CharType typ = toCharType(s[i]);
            if (transfer[st].find(typ) == transfer[st].end()) {
                return false;
            } else {
                st = transfer[st][typ];
            }
        }
        return st == STATE_INTEGER || st == STATE_POINT || st == STATE_FRACTION || st == STATE_EXP_NUMBER || st == STATE_END;
    }
};

python：

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_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
            else:
                return Chartype.CHAR_ILLEGAL
        
        transfer = {
            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
            },
            State.STATE_POINT: {
                Chartype.CHAR_NUMBER: State.STATE_FRACTION,
                Chartype.CHAR_EXP: State.STATE_EXP
            },
            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
            },
            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
            },
        }

        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]

java：

class Solution {
    public boolean isNumber(String s) {
        Map<State, Map<CharType, State>> transfer = new HashMap<State, Map<CharType, State>>();
        Map<CharType, State> initialMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
            put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
            put(CharType.CHAR_SIGN, State.STATE_INT_SIGN);
        }};
        transfer.put(State.STATE_INITIAL, initialMap);
        Map<CharType, State> intSignMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
            put(CharType.CHAR_POINT, State.STATE_POINT_WITHOUT_INT);
        }};
        transfer.put(State.STATE_INT_SIGN, intSignMap);
        Map<CharType, State> integerMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_INTEGER);
            put(CharType.CHAR_EXP, State.STATE_EXP);
            put(CharType.CHAR_POINT, State.STATE_POINT);
        }};
        transfer.put(State.STATE_INTEGER, integerMap);
        Map<CharType, State> pointMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
            put(CharType.CHAR_EXP, State.STATE_EXP);
        }};
        transfer.put(State.STATE_POINT, pointMap);
        Map<CharType, State> pointWithoutIntMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
        }};
        transfer.put(State.STATE_POINT_WITHOUT_INT, pointWithoutIntMap);
        Map<CharType, State> fractionMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_FRACTION);
            put(CharType.CHAR_EXP, State.STATE_EXP);
        }};
        transfer.put(State.STATE_FRACTION, fractionMap);
        Map<CharType, State> expMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
            put(CharType.CHAR_SIGN, State.STATE_EXP_SIGN);
        }};
        transfer.put(State.STATE_EXP, expMap);
        Map<CharType, State> expSignMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
        }};
        transfer.put(State.STATE_EXP_SIGN, expSignMap);
        Map<CharType, State> expNumberMap = new HashMap<CharType, State>() {{
            put(CharType.CHAR_NUMBER, State.STATE_EXP_NUMBER);
        }};
        transfer.put(State.STATE_EXP_NUMBER, expNumberMap);

        int length = s.length();
        State state = State.STATE_INITIAL;

        for (int i = 0; i < length; i++) {
            CharType type = toCharType(s.charAt(i));
            if (!transfer.get(state).containsKey(type)) {
                return false;
            } else {
                state = transfer.get(state).get(type);
            }
        }
        return state == State.STATE_INTEGER || state == State.STATE_POINT || state == State.STATE_FRACTION || state == State.STATE_EXP_NUMBER || state == State.STATE_END;
    }

    public CharType toCharType(char ch) {
        if (ch >= '0' && ch <= '9') {
            return CharType.CHAR_NUMBER;
        } else if (ch == 'e' || ch == 'E') {
            return CharType.CHAR_EXP;
        } else if (ch == '.') {
            return CharType.CHAR_POINT;
        } else if (ch == '+' || ch == '-') {
            return CharType.CHAR_SIGN;
        } else {
            return CharType.CHAR_ILLEGAL;
        }
    }

    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
    }

    enum CharType {
        CHAR_NUMBER,
        CHAR_EXP,
        CHAR_POINT,
        CHAR_SIGN,
        CHAR_ILLEGAL
    }
}

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