Valid Number --01 May 2015

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.

enum lexical{ valid, space, sign, number, dot, e };

int isType(const char c){
    switch(c){
        case ' ': return 1;
        case '+': ;
        case '-': return 2;
        case '.': return 4;
        case 'e': return 5;
        default: if(c <= '9' && c >= '0')   return 3;
                 else return 0;
    }
}

bool isNumber(const char *s) {
    if(!s)   return false;
    //状态转移矩阵, -1表示非法
    int map[9][6] = {
        -1, 0, 1, 2, 3, -1,  // 0状态的转移
        -1, -1, -1, 2, 3, -1,
        -1, 8, -1, 2, 4, 5,
        -1, -1, -1, 4, -1, -1,
        -1, 8, -1, 4, -1, 5,
        -1, -1, 6, 7, -1, -1,
        -1, -1, -1, 7, -1, -1,
        -1, 8, -1, 7, -1, -1,
        -1, 8, -1, -1, -1, -1 
    };
    int state = 0;
    while(*s){
        state = map[state][isType(*s)];
        if(state == -1)   return false;
        s++;
    }
    return state == 2 || state == 4 || state == 7 || state == 8;
}