LeetCode-65. Valid Number

Validate if a given string can be interpreted as a decimal number.

Some examples:

"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
" -90e3   " => true
" 1e" => false
"e3" => false
" 6e-1" => true
" 99e2.5 " => false
"53.5e93" => true
" --6 " => false
"-+3" => false
"95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9
• Exponent - "e"
• Positive/negative sign - "+"/"-"
• Decimal point - "."

Of course, the context of these characters also matters in the input.

Update (2015-02-10):
The signature of the ​​​C++​​​ function had been updated. If you still see your function signature accepts a ​​const char *​​ argument, please click the reload button to reset your code definition.

题解：

后面的测试用例真的没意思。。

基本思路就是有限状态转换自动机， 黑色为合法状态。

删除前后的空格，进行判断。

#define INUM    1
#define IEXP    2
#define IPOINT  3
#define ISYMBOL 4
#define IERR    5

#define BEGIN   1
#define NUM     2
#define POINT   3
#define SYMBOL  4
#define EXP     5
#define ESYMBOL 6
#define ENUM    7
#define PNUM    8
#define ERR     9

class Solution {
public:
    void judge(int input, int &state) {
        switch(input){
            case INUM:
                if (state == BEGIN || state == SYMBOL || state == NUM) {
                    state = NUM;
                }
                else if (state == POINT ||state == PNUM) {
                    state = PNUM;
                }
                else if (state == ENUM || state == ESYMBOL || state == EXP) {
                    state = ENUM;
                }
                else {
                    state = ERR;
                }
                break;
                           
            case IEXP:
                if (state == NUM || state == PNUM) {
                    state = EXP;
                }
                else {
                    state = ERR;
                }
                break;
                  
            case IPOINT:
                if (state == SYMBOL || state == BEGIN) {
                    state = POINT;
                }
                else if (state == NUM) {
                    state = PNUM;
                }
                else {
                    state = ERR;
                }
                break;

            case ISYMBOL:
                if (state == BEGIN) {
                    state = SYMBOL;
                }
                else if (state == EXP) {
                    state = ESYMBOL;
                }
                else {
                    state = ERR;
                }
                break;

            case IERR:
                state = ERR;
                break;
        }
        if (state == ERR) {
            return;
        }
    }
    void getInput(vector<int> &input, string s) {
        for (int i = 0; i < s.length(); i++) {
            if (s[i] >= '0' && s[i] <= '9') {
                input[i] = INUM;
            }
            if (s[i] == '-' || s[i] == '+') {
                input[i] = ISYMBOL;
            }
            if (s[i] == 'e') {
                input[i] = IEXP;
            }
            if (s[i] == '.') {
                input[i] = IPOINT;
            }
        }
    }
    bool isNumber(string s) {
        int n = s.length();
        if (n == 0) {
            return false;
        }
        int l = 0, r = n - 1;
        while (s[l] == ' ') {
            l++;
        }
        while (s[r] ==  ' ') {
            r--;
        }
        string fix = s.substr(l, r - l + 1);
        int state = BEGIN;
        int m = fix.length();
        if (m == 0) {
            return false;
        }
        vector<int> input(m, IERR);
        getInput(input, fix);
        for (int i = 0; i < m; i++) {
            judge(input[i], state);
            if (state == ERR) {
                return false;
            }
        }
        if (state == NUM || state == PNUM || state == ENUM) {
            return true;
        }
        return false;
    }
};