9/2刷题表示数值的字符串

1.表示数值的字符串
请实现一个函数用来判断字符串是否表示数值（包括整数和小数）。例如，字符串"+100"、"5e2"、"-123"、"3.1416"、"-1E-16"、"0123"都表示数值，但"12e"、"1a3.14"、"1.2.3"、"+-5"及"12e+5.4"都不是。
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/biao-shi-shu-zhi-de-zi-fu-chuan-lcof
思路：确定有限状态自动机

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_SPACE,
        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 if (ch == ' ') {
            return CHAR_SPACE;
        } else {
            return CHAR_ILLEGAL;
        }
    }

    bool isNumber(string s) {
        unordered_map<State, unordered_map<CharType, State>> transfer{
            {
                STATE_INITIAL, {
                    {CHAR_SPACE, 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},
                    {CHAR_SPACE, STATE_END},
                }
            }, {
                STATE_POINT, {
                    {CHAR_NUMBER, STATE_FRACTION},
                    {CHAR_EXP, STATE_EXP},
                    {CHAR_SPACE, STATE_END},
                }
            }, {
                STATE_POINT_WITHOUT_INT, {
                    {CHAR_NUMBER, STATE_FRACTION},
                }
            }, {
                STATE_FRACTION,
                {
                    {CHAR_NUMBER, STATE_FRACTION},
                    {CHAR_EXP, STATE_EXP},
                    {CHAR_SPACE, STATE_END},
                }
            }, {
                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},
                    {CHAR_SPACE, STATE_END},
                }
            }, {
                STATE_END, {
                    {CHAR_SPACE, STATE_END},
                }
            }
        };

        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;
    }
};