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class Solution {//finite state machine//status 1 => 小数点前面的部分//status 2 => 小数点后到'e'前面的部分//status 3 => e后面的科学计数法部分//should practice couple times morepublic:	bool isNumber(const char *s) {		// Start typing your C/C++ solution below		// DO NOT write int main() function		bool bIntNum = false;		int nCurState = 1;		while (true)		{			if (nCurState == 1)			{				while (*s == ' ')					s++;				if (*s == '+' || *s == '-')					s++;				if (*s >= '0' && *s <= '9')				{					while (*s >= '0' && *s <= '9')						s++;					bIntNum = true;				}				if (*s == '.' /*&& bIntNum*/) //.34 true				{					nCurState = 2;					s++;					continue;				}				else if (*s == 'e' && bIntNum)//go to state 3, there must have bIntNum before				{					nCurState = 3;					s++;					continue;				}				while (*s == ' ')					s++;				return (bIntNum && *s == 0);			}			else if (nCurState == 2)//1. true			{				//bIntNum = false;				if (*s >= '0' && *s <= '9')				{					while (*s >= '0' && *s <= '9')						s++;					bIntNum = true;				}				if (*s == 'e' && bIntNum)//go to state 3, there must have bIntNum before				{					nCurState = 3;					s++;					continue;				}				while (*s == ' ')					s++;				return (bIntNum && *s == 0);//if there is no e, then there must have bIntNum, such as ".23" or "1."			}			else//nCurState 3 need judge if there is bIntNum again, because "1e" is illegal			{				bIntNum = false;				if (*s == '+' || *s == '-')					s++;				if (*s >= '0' && *s <= '9')				{					while (*s >= '0' && *s <= '9')						s++;					bIntNum = true;				}				while (*s == ' ')					s++;				return (*s == 0 && bIntNum);			}		}	}};

second time

class Solution {//finite automatapublic:    vector
   
    
      > transTable;    int inputType(char a)    {        if(a == ' ') return 0;        else if(a == '+' || a == '-') return 1;        else if(a >= '0' && a <= '9') return 2;        else if(a == '.') return 3;        else if(a == 'e') return 4;        else return 5;//illegal input    }    void initTransTable()    {        transTable.resize(9, vector
     
      (5, -1));        transTable[0][0] = 0;        transTable[0][1] = 1;        transTable[0][2] = 2;        transTable[0][3] = 7;        transTable[7][2] = 3;        transTable[1][2] = 2;        transTable[1][3] = 7;        transTable[2][2] = 2;        transTable[2][0] = 6;        transTable[2][3] = 3;        transTable[2][4] = 4;        transTable[3][2] = 3;        transTable[3][4] = 4;        transTable[3][0] = 6;        transTable[4][1] = 8;        transTable[8][2] = 5;        transTable[4][2] = 5;        transTable[5][2] = 5;        transTable[5][0] = 6;        transTable[6][0] = 6;    }    bool isNumber(const char *s) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(s == NULL) return false;        initTransTable();        int curState = 0;        while(*s != '\0')        {            int curInput = inputType(*s);            if(curInput == 5) return false;            curState = transTable[curState][curInput];            if(curState == -1) return false;            s++;        }        if(curState == 2 || curState == 3 || curState == 5 || curState == 6) return true;        else return false;     }};
     
    
   

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