Java IF语句（提高了算法效率）

Question

I used method a that counts the amount of possible choices for getting like number 10 with numbers that are from 0 to 6. Problem is that it just takes too much time when x is like 50 or something. I just need some tips what I should do to make this faster.

Code

public static int count(int x) {
    if (x < 0) {
        return 0;
    }
    if (x == 0) {
        return 1;
    }

    int result = 0;
    for (int i = 1; i <= 6; i++) {
        result += count(x - i);
    }
    return result;
}

Answer 1

This is a variation on Fibonacci except it is the sum of the last six values instead.

You can use a plain loop which will be faster than memorisation (the first time)

public static long count(int x) {
    long a=0, b=0, c=0, d=0, e=0, f=1;
    while(x-- > 0) {
       long sum = a + b + c + d + e + f;
       a = b; b = c; c = d; d = e; e = f;
       f = sum;
    }
    return f;
}

If you call this repeatedly you may as well store all the values in the int range which is likely to be less than 30 the first time and retrieve these values after that.