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 more
public:
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 automata
public:
vector<vector<int> > 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<int>(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;
}
};