Question

Given two arrays

int arr1[n]
int arr2[m]

where n > m

Need to write a union of two arrays into one.

For example, if the input arrays are:

   int arr1[] = {1, 3, 4, 5, 7}
   int arr2[] = {2, 3, 5, 6}

Then program should create new array Union as {1, 2, 3, 4, 5, 6, 7}

Implementation can be in C# or Java.

In order to solve it first of all need to to sort the arrays using Merge Sort
and then do the union

I looked in the net but did not find the elegant way . Every code that I looked
was full of IF’s.

Please advice what is the most quick and elegant way to do it

Answer 1

You are correct that merging the two lists as is done in Merge Sort is the most efficient thing to do. This assumes that the two lists are already sorted, as in your example. Here is an example of how to implement merge:

function merge(left,right)
    var list result
    while length(left) > 0 or length(right) > 0
        if length(left) > 0 and length(right) > 0
            if first(left) ≤ first(right)
                append first(left) to result
                left = rest(left)
            else
                append first(right) to result
                right = rest(right)
        else if length(left) > 0
            append first(left) to result
            left = rest(left)
        else if length(right) > 0
            append first(right) to result
            right = rest(right)
    end while
    return result

From here, simply do not include repeats in the final output.