Finding the difference between two int arrays

Question

I am having trouble figuring out the algorithm that will find the differences between two integer arrays. I already have a sorting method that it will be ran through so the numbers are in ascending order.

For example:

SetX = { 1, 2, 3, 4, 5 }

SetY = { 0, 2, 4, 6 }

The return should be the numbers in SetX that does not appear in SetY.

so resultSet = { 1, 3, 5 }

Sometimes I get the correct answer if I do small arrays but if I do arrays that are 4 or more Integers long it gives me the wrong return.

Can someone look over my code and tell me what I am doing wrong?

public static int firstFruit(int[] setX, int usedSizeSetX, int[] setY, int usedSizeSet2, int[] resultSet) {
    int a = 0, b = 0, c = 0;

    while( a < usedSizeSetX && b < usedSizeSetY){
        if(setX[a] == setY[b]) {
            a++;
        } else if(setX[a] == setY[b]){
            b++;
        } else {
            resultSet[c++] = setX[a++];
            b++;
        }
    }
    return c;
}

Can you give some example inputs where it is giving the wrong answer? — BretC, Dec 06 '16 at 16:26
your first two checks are exactly the same. You'll never get into the second conditional... — jgitter, Dec 06 '16 at 16:27
[Here](https://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html) there is a list of all the methods the class **Array** offers. For each element in one array you could use binsearch to find if it appears in the other array. — , Dec 06 '16 at 16:29
What is the logic behind your algorithm? I notice that you check for the same condition twice .. in `if` and in `else if` (`setX[a] == setY[b]`) .. this doesn't make sense .. may be a typo? — PKey, Dec 06 '16 at 16:34

score 1 · Accepted Answer · answered Dec 06 '16 at 16:32

1

I think your conditionals are a little FUBAR. The processing should be:

If setX[a] > setY[b] -> b++
If setX[a] < setY[b] -> a++
Else -> add setX[a] to the result, a++, b++

answered Dec 06 '16 at 16:32

jgitter

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could you explain it in layman's terms please. I think the multiple counters are confusing me. – Pableto Dec 06 '16 at 16:46
@Pableto I'd suggest taking the example arrays you give and walking through it yourself. It can be useful to write out every step on a piece of paper. – AndyReifman Dec 06 '16 at 18:05

Finding the difference between two int arrays

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