leetcode-go/leetcode/hard/65.valid-number.java

class Solution {
    // Numbers 0-9
    // Exponent - "e"
    // Positive/negative sign - "+"/"-"
    // Decimal point - "."
    public boolean isNumber(String s) {
        // Finite automaton
        // State No. | Discription
        // ----------+------------
        //    -1     | Invalid state
        //     0     | Initial state
        //     1     | Input sign
        //     2     | Input digit
        //     3     | Input dot
        //     4     | Input digit and dot (like .33 or 33. or 3.3)
        //     5     | Input exp
        //     6     | Input sign after exp
        //     7     | Input digit after exp
        //     8     | Input space after valid number
        // Input state:
        // ERROR, SPACE, SIGN, DIGIT, DOT, EXP
        // Trans table:
        //     \input| ERR SPA SGN DIG DOT EXP
        // state\    |
        // ----------+------------------------
        //      0    |  -1   0   1   2   3  -1
        //      1    |  -1  -1  -1   2   3  -1
        //      2    |  -1   8  -1   2   3   5
        //      3    |  -1  -1  -1   4  -1   5
        //      4    |  -1   8  -1   4  -1   5
        //      5    |  -1  -1   6   7  -1  -1
        //      6    |  -1  -1  -1   7  -1  -1
        //      7    |  -1   8  -1   7  -1  -1
        //      8    |  -1   8  -1  -1  -1  -1
        char[] num = s.toCharArray();
        int[][] stateTable = new int[][] {
            {-1,  0,  1,  2,  3, -1}, // 0
            {-1, -1, -1,  2,  3, -1}, // 1
            {-1,  8, -1,  2,  4,  5}, // 2
            {-1, -1, -1,  4, -1, -1}, // 3
            {-1,  8, -1,  4, -1,  5}, // 4
            {-1, -1,  6,  7, -1, -1}, // 5
            {-1, -1, -1,  7, -1, -1}, // 6
            {-1,  8, -1,  7, -1, -1}, // 7
            {-1,  8, -1, -1, -1, -1}  // 8
        };
        int state = 0;
        for (int i = 0; i < num.length; i++) {
            int input = 0; // ERROR
            if (num[i] == ' ') input = 1; // SPACE
            else if (num[i] == '+' || num[i] == '-') input = 2; // SIGN
            else if ('0' <= num[i] && num[i] <= '9') input = 3; // DIGIT
            else if (num[i] == '.') input = 4; // DOT
            else if (num[i] == 'e' || num[i] == 'E') input = 5; // EXP
            state = stateTable[state][input];
            if (state == -1) return false;
        }
        return state == 2 || state == 4 || state == 7 || state == 8;
    }
}