Question

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Horner's recursive algorithm for fractional part – Java

I am writing a program for Horne’r Algorithm, and I will be honest, I do not have much experience with recursion. I have this method set up to accept a fraction only (there is another method which accepts and returns the whole number) and it will return the result converted from base ‘r’ to base 10. I am unsure why, but the method does not seem to be going through the final iteration. Any suggestions as to what I need to do to correct this problem would be greatly appreciated.

(ex: c = 011, xFinal = 2, i = 2)
Expected answer = .375
Actual answer returned = .75

public static double getHornerFraction(long[] c, int xFinal, int i) {
    if (i == 0) {
        return ((double)c[i])/xFinal; 
    }
    return (getHornerFraction(c, xFinal, i-1) + c[i])/xFinal;
}

Answer 1

From looking at what you specified and what you expect, I think the problem is that you are walking the array c in the wrong direction or otherwise specifying it incorrectly. I think that what you want to do is actually walk the array from index 0 to c.length.

public static double getHornerFraction(long[] c, int xFinal, int i) {
    if (i == c.length) {
        return 0;
    }
    return (getHornerFraction(c, xFinal, i+1) + c[i])/xFinal;
}

Call the above function with c = {0,1,1}, xFinal = 2, i = 0 and it should give what you expect.