500th Video Contest Solution

Solve.java

class Solve {
    
    public static int parseInt(char a) {
        int num = (int)a;
        if (num < (int)'0' || num > (int)'9') {
            throw new RuntimeException("Parse error");
        }
        return num - (int)'0';
    }

    public static boolean is_solution(String key) {
        if (key.length() != 11) return false;
        int a = parseInt(key.charAt(0));
        int b = parseInt(key.charAt(1));
        int c = parseInt(key.charAt(2));
        int d = parseInt(key.charAt(3));
        int e = parseInt(key.charAt(4));
        int f = parseInt(key.charAt(5));
        int g = parseInt(key.charAt(6));
        int h = parseInt(key.charAt(7));
        int i = parseInt(key.charAt(8));
        int j = parseInt(key.charAt(9));
        int k = parseInt(key.charAt(10));
        try {
            if (j / b != f) return false;
            if (c / i != b) return false;
            if (d / e != a) return false;
            if (h / e != b) return false;
            if (b % c != e) return false;
            if (f % d != j / d) return false;
            if (k % i != j) return false;
            if (k % d != a * b) return false;
            if (e - g != i) return false;
            if (d - g != c) return false;
            if (k + a != d) return false;
            if (a * b != e * i) return false;
        } catch (ArithmeticException ex) {
            return false;
        }
        return true;
    }
    
    public static void main(String[] args) {
        // this would greatly benefit from recursion or more mathematical reasoning
        for (int a = 0; a < 10; a++) {
            for (int b = 0; b < 10; b++) {
                for (int c = 1; c < 10; c++) {
                    for (int d = 0; d < 10; d++) {
                        for (int e = 1; e < 10; e++) {
                            if (d / e != a) continue;
                            if (b % c != e) continue;
                            for (int f = 0; f < 10; f++) {
                                for (int g = 0; g < 10; g++) {
                                    if (d - g != c) continue;
                                    for (int h = 0; h < 10; h++) {
                                        for (int i = 0; i < 10; i++) {
                                            for (int j = 0; j < 10; j++) {
                                                for (int k = 0; k < 10; k++) {
                                                    String s = "" + a + b + c + d + e + f + g + h + i + j + k;
                                                    if (is_solution(s)) {
                                                        System.out.println(s);
                                                    }
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    
}