Valid Number

Description:

Validate if a given string is numeric.

Example

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

Solution:

class Solution {
public:
	/**
	 * @param s the string that represents a number
	 * @return whether the string is a valid number
	 */
	bool isNumber(string& s) {
		enum InputType {
			SPACE, // 0
			SIGN, // 1
			DIGIT, // 2
			DOT, // 3
			EXPONENT, // 4
			TYPE_SIZE // 5
		};
		const int table[][TYPE_SIZE] = {
			0, 3, 1, 2, -1,
			8, -1, 1, 4, 5,
			-1, -1, 4, -1, -1,
			-1, -1, 1, 2, -1,
			8, -1, 4, -1, 5,
			-1, 6, 7, -1, -1,
			-1, -1, 7, -1, -1,
			8, -1, 7, -1, -1,
			8, -1, -1, -1, -1,
		};
		int state = 0;
		for (auto ch : s) {
			int inputType;
			if (ch == ' ' || ch == '\t')
				inputType = SPACE;
			else if (ch == '+' || ch == '-')
				inputType = SIGN;
			else if (ch >= '0' && ch <= '9')
				inputType = DIGIT;
			else if (ch == '.')
				inputType = DOT;
			else if (ch == 'e' || ch == 'E')
				inputType = EXPONENT;
			else return false;
			state = table[state][inputType];
			if (state == -1) return false;
		}
		return state == 1 || state == 4 || state == 7 || state == 8;
	}
};