SRM 736 Div1 Easy

DigitRotation.java

public class DigitRotation {
    public int sumRotations(String X) {
        int[] digits = new int[X.length()];
        for (int i = 0; i < digits.length; i++) digits[i] = X.charAt(i) - '0';

        final long n = digits.length;
        final int mod = 998244353;
        long[] pow = new long[digits.length];
        pow[digits.length - 1] = 1;
        for (int i = digits.length - 2; i >= 0; i--) {
            pow[i] = pow[i+1] * 10 % mod;
        }
        long ans = 0;
        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += digits[i] * pow[i] % mod;
        }
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                for (int k = j + 1; k < n; k++) {
                    if (i == 0 && digits[k] == 0) continue;
                    ans += digits[k] * pow[i] % mod;
                    ans += digits[i] * pow[j] % mod;
                    ans += digits[j] * pow[k] % mod;
//                    dump(i, j, k);
                    ans += sum;
                    ans -= digits[i] * pow[i] % mod;
                    ans -= digits[j] * pow[j] % mod;
                    ans -= digits[k] * pow[k] % mod;
                    ans %= mod;
                }
            }
        }
        return (int)((ans % mod + mod) % mod);
    }

    static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); }
    static void swap(int[] xs, int i, int j) { int t = xs[i]; xs[i] = xs[j]; xs[j] = t; }
    static void swap(long[] xs, int i, int j) { long t = xs[i]; xs[i] = xs[j]; xs[j] = t; }
    static long gcd(long n, long r) { return r == 0 ? n : gcd(r, n % r); }
    static long lcm(long n, long r) { return n / gcd(n, r) * r; }
}