Loops and arrays not following through

Question

int [] f = {1,2,3,4,5,5,4,3,2,1};
int [] b = {6,1};
System.out.println(Arrays.toString(hide(f,b)));

public static int [] hide(int [] front, int [] back) {
    int temp;
    int extraTemp;
    int nextTemp = 0;

    int [] hiddenAt = new int[front.length];
    //int [] shownAt = new int[front.length];

    for(int x = 0; x < front.length; x++){
        for(int y = 0; y <= back.length; y++){
            temp = x;
            if ((back.length > front.length) || (front[x] < 0 || back[y] < 0) || (front.length < 1 || back.length < 1)) {
                System.exit(0);
            }

            if (y < back.length - 1){
            nextTemp = Math.abs(back[y + 1] - front[x + 1]);
            }
            else {
                nextTemp = 0;
            }

            if (front[x] > back[y]) {
                System.out.println(temp);
            }
            else if (front[x] < back[y] && y >= back.length - 1 ) {
                extraTemp = back[y] - front[x];

                if (extraTemp > nextTemp){
                    extraTemp = nextTemp;
                }
                System.out.println(extraTemp);
            }
            else if (front[x] < back[y]) {
                extraTemp = back[y] - front[x];

                if (extraTemp > nextTemp){
                    extraTemp = nextTemp;
                }
                System.out.println(extraTemp);
            }
        }
    }
    return hiddenAt;
}

The println 's are being substituted in to see the values that are being produced. They will be hiddenAt[z] = temp; when I figure out the values to be correct.

I need it to compare front[0] with back[0] then front[1] with back[1] , etc. After that, it will shift over one: front[1] with back[1] then front[2] with back[2] until the end of front[] . I want to find out where the lowest difference is. (In this case when the number in the []'s is 4 and 5.)

I get two errors, one saying line 39 if ((back.length > front.length) || (front[x] < 0 || back[y] < 0) || (front.length < 1 || back.length < 1)) { System.exit(0); }

is wrong and that line 9 is wrong as well. public class 2 { public static void main(String[] args) {

    int [] f = {1,2,3,4,5,5,4,3,2,1};
    int [] b = {6,1};
    System.out.println(Arrays.toString(hide(f,b)));
}

the exact error is:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 2
at hw2.hide(hw2.java:39)
at hw2.main(hw2.java:9)

Answer 1

Your problem is that Array index out of bounds so you are trying to access an element that doesn't exist.

in the line if ((back.length > front.length) || (front[x] < 0 || back[y] < 0) || (front.length < 1 || back.length < 1)) { where you say back[y] < 0 your for statement goes to <= back.length

for(int y = 0; y <= back.length; y++){

so back has a length of 2(has 2 elements) however you will be doing this loop three times 0,1,2 on the third loop there is no back[2] as back[0] = 6 and back[1] = 1 .

so changing for(int y = 0; y <= back.length; y++){ to for(int y = 0; y < back.length; y++){ will fix this particular error

Remember, lengths start at 1(if it has elements) indexes start at 0.

Answer 2

This is your 2nd array problem:

        if (y < back.length - 1){
        nextTemp = Math.abs(back[y + 1] - front[x + 1]);
        }
        else {
            nextTemp = 0;
        }

While you check that y < back.length - 1 you do not do the same for x .

So, you need if (y < back.lenth-1 && x < front.length-1) assuming that you do want to reference front[x+1] .