Leetcode 65 Valid Number DFA有限状态机

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

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.

判断数字的合法性

刚开始是把它作为一道细节较多的模拟题做的，通过后去discuss看了一下，果然有优美的解答！

用有限状态机DFA解决，将每一位看成一种状态转移条件，每次读取的一位，就根据转移矩阵进行状态转移，若转移到不合法的状态则返回false。

思路简单优美，不用考虑多余的细节问题，刷了这么多leetcode，这题真的眼前一亮！

具体的状态说明可以看这篇博客

class Solution {
public:
    bool isNumber(string s) {
        int mp[9][6]={
            {-1,  0,  1,  2, -1,  3},
            {-1, -1, -1,  2, -1,  3},
            {-1, -1, -1, -1, -1,  4},
            {-1,  5, -1,  4,  6,  3},
            {-1,  5, -1, -1,  6,  4},
            {-1,  5, -1, -1, -1, -1},
            {-1, -1,  7, -1, -1,  8},
            {-1, -1, -1, -1, -1,  8},
            {-1,  5, -1, -1, -1,  8}
        };
        int now=0;
        for(int i=0;i='0' && s[i]<='9')
                        now=mp[now][5];
                    else
                        now=mp[now][0];
                }
            }
            if(now==-1) return false;
        }
        return now==3 || now==4 || now==5 || now==8 ;
    }
};