LeetCode: Valid Number

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.

---

Referred to the discussion in the forum, this problem can be solved via finite automata.

C++ Code:

/*
 * func: valid_number
 * goal: to check if the current string is a valid number
 * @param s: input string
 * return: true or false
 */
bool valid_number(const char *s){
    enum InputType{
        INVALID,   //0
        SPACE,     //1
        SIGN,      //2
        DIGIT,     //3
        DOT,       //4
        EXPONENT,  //5
        NUM_INPUTS //6
    };
    int transition_table[][NUM_INPUTS] = {
      -1,  0,  3,  1,  2, -1,
      -1,  8, -1,  1,  4,  5,
      -1, -1, -1,  4, -1, -1,
      -1, -1, -1,  1,  2, -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 != '\0'){
        InputType input_type = INVALID;
        if(isspace(*s)){
            input_type = SPACE;
        }else if(*s == '+' || *s == '-'){
            input_type = SIGN;
        }else if(isdigit(*s)){
            input_type = DIGIT;
        }else if(*s == '.'){
            input_type = DOT;
        }else if(*s == 'e' || *s == 'E'){
            input_type = EXPONENT;
        }
        
        state = transition_table[state][input_type];
        
        if(state == -1){
            return false;
        }
        ++s;
    }
    
    return state == 1 || state == 4 || state == 7 || state == 8;
}

Python Code:

# func: to test the input string is in valid number format
# @param s: input string
# @return: True or False
def valid_number(s):
    # 0 ==> INVALID
    # 1 ==> SPACE
    # 2 ==> SIGN
    # 3 ==> DIGIT
    # 4 ==> DOT
    # 5 ==> EXPONENT
    transition_table = [[-1, 0, 3, 1, 2, -1],
                        [-1, 8, -1, 1, 4, 5],
                        [-1, -1, -1, 4, -1, -1],
                        [-1, -1, -1, 1, 2, -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]]
    state = 0
    index = 0
    while index < len(s):
        input_type = 0
        if s[index] == ' ':
            input_type = 1
        elif s[index] == '+' or s[index] == '-':
            input_type = 2
        elif s[index] in '0123456789':
            input_type = 3
        elif s[index] == '.':
            input_type = 4
        elif s[index] == 'e' or s[index] == 'E':
            input_type = 5

        state = transition_table[state][input_type]

        if state == -1:
            return False
        else:
            index += 1

    return state == 1 or state == 4 or state == 7 or state == 8

Reference Link:

1. [closed] Valid Number - LeetCode http://discuss.leetcode.com/questions/241/valid-number