Difference between elements in one array in Java

Question

I'm learning Java and I trying to construct a method for my homework. It takes as argument an Array and returns the difference between its elements (as absolute value).

For example: array {7,8,5,7,2}

the difference between elements 0 and 1 is 1 (=7−8)

the difference between elements 1 and 2 is 3 (=8−5)

the difference between elements 2 and 3 is 2 (=5-7)

the difference between elements 3 and 4 is 5 (=7−2)

the difference between elements 4 and 0 is 5 (=2-7)

If there are multiple candidates the method will return the one with the greatest index. In this example, the last one. If the array is empty, then the method must return −1.

I have some problems in my code (as you can see) and the biggest one is that my method returns only the last diff and not the biggest one with the higher index. Can someone help me? I'm not figuring out how to solve this problem.

public static int MaxDiff(int[] array){

        int diff = 0;

        if (array.length == 0){   // Checks for empty array
            return -1;
        }

        for (int i = 0; i <= array.length; ++i){

            if(i == array.length){
                diff = Math.abs(array[i] - array[0]);
            } else {
                diff = Math.abs(array[i] - array[i+1]); // Mistake. Can be
                                                        // bigger than array
            }
        }

        return diff;
    }

the code you showed will give you ArrayIndexOutOfBound Exception — singhakash
– singhakash, Commented Nov 1, 2015 at 17:56
Also: Don't use an if inside the loop to check, if it's the last iteration. Just add the code after the loop instead. — fabian
– fabian, Commented Nov 1, 2015 at 17:59

Litle Dev · Accepted Answer · 2015-11-01 18:04:49Z

2

I have changed a little and then your code works correctly.

public static int MaxDiff(int[] array){

    int diff = 0;

    if (array.length == 0){ 
        return -1;
    }

    int max = 0;
    for (int i = 0; i < array.length-1; ++i){

        diff = Math.abs(array[i] - array[i+1]);
        if(max < diff)
            max = diff;
    }

    return max;
}

answered Nov 1, 2015 at 18:04

Litle Dev

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Comments

rajuGT · Accepted Answer · 2015-11-01 18:04:29Z

0

Create one instance variable maxDiff and update if you find diff greater than current computation diff in the loop. like

maxDiff = diff > maxDiff ? diff : maxDiff;

Finally return the maxDiff;

public static int MaxDiff(int[] array){

         //create a variable to hold maxDiff;
        int maxDiff = 0;
        int diff = 0;

        if (array.length == 0){   // Checks for empty array
            return -1;
        }

        //Change from <= to < (otherwise you will get ArrayIndexOutOfBound exception
        for (int i = 0; i < array.length; ++i){

            if(i == array.length -1){
                diff = Math.abs(array[i] - array[0]);
            } else {
                diff = Math.abs(array[i] - array[i+1]); // Mistake. Can be
                                                        // bigger than array
            }
            //check for max
            maxDiff = diff > maxDiff ? diff : maxDiff;
        }

        return maxDiff;
    }

edited Nov 1, 2015 at 18:04

answered Nov 1, 2015 at 18:01

rajuGT

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2 Comments

Héctor Valls Over a year ago

i will never be == to array.length

rajuGT Over a year ago

Yep. I just updated main part of the program. thanks.

yannick1976 · Accepted Answer · 2015-11-01 18:05:59Z

0

You have to set diff only if it is bigger than it already is.

int newDiff;
if(i == array.length - 1){
    newDiff = Math.abs(array[i] - array[0]);
} else {
    newDiff = Math.abs(array[i] - array[i+1]);
}
if(newDiff > diff)
    diff = newDiff;

Also as @singhakash says the index of the last element of an array of size n is n - 1, not n.

edited Nov 1, 2015 at 18:05

answered Nov 1, 2015 at 17:59

yannick1976

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