Anyone know how I can improve my score (83.33) to 100.00. I've done all the optimisations I could think of..

class Result {

/*
 * Complete the 'legoBlocks' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER n (width)
 *  2. INTEGER m (height)
 */

// Cache previous C(n,m) calculations - All Combinations to build a wall with Brick sizes [1,4]
// Cache previous N(n,m) calculations - All Combinations to build a legitimate wall with no breaks

public static Map<String, BigInteger> C_n_m = new HashMap<>();
public static Map<String, BigInteger> N_n_m = new HashMap<>();
public static BigInteger modulo = BigInteger.valueOf(1_000_000_007);

public static BigInteger noBreakWalls(int n, int m) {
    String key = n + "," + m;
    if (N_n_m.containsKey(key)) return N_n_m.get(key);
    BigInteger sum = buildAnyWall(n, m);
    for (int i=1; i < n ; i++) {
        sum = sum.subtract(buildAnyWall(n-i, m).multiply(noBreakWalls(i, m))); 
    }
    sum = sum.mod(modulo);
    N_n_m.put(key, sum);
    return sum;
}

public static BigInteger buildAnyWall(int n, int m) {
    String key = n + "," + m;
    if (C_n_m.containsKey(key)) return C_n_m.get(key);
    if (n < 5) {
        BigInteger basecase = BigInteger.valueOf(2).modPow(BigInteger.valueOf(m*(n-1)), modulo);
        C_n_m.put(key, basecase);
        return basecase;
    } else {
        BigInteger row = buildAnyWall(n-1, 1)
                            .add(buildAnyWall(n-2, 1))
                                .add(buildAnyWall(n-3, 1))
                                    .add(buildAnyWall(n-4, 1))
                                        .modPow(BigInteger.valueOf(m), modulo);
        C_n_m.put(key, row);
        return row;
    }
}

public static int legoBlocks(int n, int m) {
    return noBreakWalls(n, m).intValue();
}

}