Java - Adding contents of two unequal arrays

Question

Lets say array one [2/3, 0, -1, 0, 7/2] and array two [0, 0, -2/3, 1, 0, 0] so I want my result array to be [0, 2/3, -2/3, 0, 0, 7/2]. The result array length will be the max length between the two arrays. How can I do this in Java?

Pretty much I want the specific index locations to add each other however I don't know how to do this with unequal arrays.

Edit: It adds the locations and anything that is unmatched is left untouched in the largest array. [0, 0, -2/3, 1, 0, 0] has location 0, 1, 2, 3, 4, 5 and array [2/3, 0, -1, 0, 7/2] has locations that coincide with the larger array as 1, 2, 3, 4, 5 so I want the same location values to be added and placed into the resultant array. I created a new resultant array and set it equal to the largest array so all that has to be done is the adding of similar location values.

What exactly do you want to have happen when the two arrays have different lengths? Should the unmatched numbers at the end of the longer array go at the end of the new array? Should the end of the new array just have zeros? You need to think this part through before we can help you implement it. — musical_coder
– musical_coder, Commented Oct 14, 2013 at 1:10
Do one loop with index that runs on the range of the shorter array and adds the numbers. Then do another loop that run on what is left of the other array. — Eran
– Eran, Commented Oct 14, 2013 at 1:10

Jose · Accepted Answer · 2013-10-14 02:09:42Z

Here is an elaborate and easy to understand way that I've devised:

What it does it it adds the last elements of the arrays together and moves backwards from there; if one array ends before the other, it just substitutes the value of the non-existent element with zero, then adds them:

public class ArrayAddition
{
public static void main(String[] args)
{
    double array1[] = {2./3, 0, -1, 0, 7./2}; // first array
    double array2[] = {0, 0, -2./3, 1, 0, 0}; // second array
    int length = Math.max(array1.length, array2.length); // length of longest array
    double newArray[] = new double[length]; // result must be length of longest array

    int index1 = array1.length - 1; // last element of first array
    int index2 = array2.length - 1; // last element of second array
    int indexRes = length - 1;      // result will be placed in last spot of result

    for (int i = length -1; i >= 0; i--) // adds elements of two arrays together bckwrd
    {

        double val1, val2;     // value holders for array elements

        try  // try to get value of the array 1 at certain position
        {
            val1 = array1[index1];
        }
        catch(ArrayIndexOutOfBoundsException e)  // if empty, make it zero
        {
          val1 = 0;
        }

        try   // try to get value of array 2 at certain position
        {
            val2 = array2[index2];
        }
        catch(ArrayIndexOutOfBoundsException e) // if empty make it zero
        {
            val2 = 0;
        }

        newArray[indexRes] = val1 + val2; // array[?] result is val1 + val 2
        index1--;  // decrement to the next lower value
        index2 --; // decrement to the next lower value
        indexRes--; // go the next lower spot


    }

    for (int i = 0; i < newArray.length; i ++)  // this loop prints out the results
        System.out.println(newArray[i]);

}

}

You need to enter your values as doubles or the answers will be incorrect (2./3 instead of 2/3)

0.0
0.6666666666666666
-0.6666666666666666
0.0 
0.0
3.5

Answers will be in decimal form, for obvious reasons (if answer is 2 / 3, it actually divides 2 by 3, still the correct answer, you can convert it back)

Hopefully this helps! :)

ug_ · Accepted Answer · 2013-10-14 01:22:41Z

0

Go through your arrays starting at the end and add the 2 values putting them into a new array with the size of the largest array.

int a = arrayA.length-1;
int b = arrayB.length-1;

double [] result = new double[Math.max(arrayA.length, arrayB.length)];
double sum = 0;
while(a >= 0 || b >= 0) {
    if(a>=0) sum+=arrayA[a];
    if(b>=0) sum+=arrayB[b];

    result[Math.max(a, b)] = sum;
    sum = 0;
    a--;
    b--;
}

answered Oct 14, 2013 at 1:22

ug_

11.5k2 gold badges37 silver badges56 bronze badges

Comments

Jay Nebhwani · Accepted Answer · 2013-10-14 01:24:04Z

0

This should do it. Note that this code is missing the declarations of the array variables.

if (array1.length > array2.length)
  array3 = addArrays(array1, array2);
else
  array3 = addArrays(array2, array1);


int [] addArrays(longArray, shortArray) {
  int index;
  for (index = 0; index < longArray.length - shortArray.length; index++) {
    array3[index] = longArray[index] + 0;
  }
  for (int i = 0; i < shortArray.length; i++, index++) {
    array3[index] = longArray[index] + shortArray[i];
  }
  return array3;
}

answered Oct 14, 2013 at 1:24

Jay Nebhwani

9767 silver badges11 bronze badges

Comments

Naddy · Accepted Answer · 2013-10-14 01:36:56Z

import java.util.Scanner;

public class ArrayAdd {
    public static void main(String args[]) {
        Scanner a = new Scanner(System.in);
        int m = a.nextInt();// First array's size
        int n = a.nextInt();// Second array's size
        int arr1[] = new int[m];
        int arr2[] = new int[n];
        for (int i = 0; i < m; i++) {
            arr1[i] = a.nextInt();
        }
        for (int i = 0; i < n; i++) {
            arr2[i] = a.nextInt();
        }
        a.close();
        if (m < n) {
            int difference = n - m;
            int arr3[] = new int[n];
            for (int i = 0; i < n; i++) {
                if (i < difference) {
                    arr3[i] = arr2[i];
                } else {
                    arr3[i] = arr1[i-difference] + arr2[i];
                }
                System.out.println(arr3[i]);
            }
        } else {
            int difference = m - n;
            int arr3[] = new int[m];
            for (int i = 0; i < m; i++) {
                if (i < difference) {
                    arr3[i] = arr1[i];
                } else {
                    arr3[i] = arr1[i] + arr2[i-difference];
                }
                System.out.println(arr3[i]);
            }
        }

    }
}

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