Merge two arrays into one

There are 2 sorted arrays of size m and m+n, respectively.

First array (of size m) has m elements and the Second array (of size m+n) has only n elements (last m positions are blank).

So, the total number of elements in both the arrays is m+n (m in the first and n in the second). Write code to merge the m+n elements in the 2^nd array such that the result is sorted. If the two arrays are as below:

Then the output should be:

Solution:

Start the backward merge of array arr1 and n elements on arr2 into arr2 (Complete array, till position m+n) 

Algorithm: 1. Let a, b & c be three pointers.

• a points to last (m^th) element of arr1
• b points to n^th (last valid) element of arr2
• c points to the last empty position of arr2 (m+n)^th

2. While ( a>=0 && b>=0). i.e will we have elements in both the arrays

    If (arr1[a] > arr2[b])
        arr2[c] = arr1[a]
            a--
    else
        arr2[c] = arr2[b]
        b--
    c--

3. If a >=0 Move remaining elements from arr1 to arr2 starting from a in arr1 to position c in arr2 in backward fashion Code:

    /** size of array arr2 should be m+n (and not n) */
    void mergeIntoSecond(int * arr1, int m, int*arr2, int n)
    {
        int a=m-1, b=n-1, c=m+n-1;
        while(a>=0 && b>=0)
        {
            if(arr1[a] > arr2[b])
            {
                arr2[c] = arr1[a];
                a--;
            }
            else
            {
                arr2[c] = arr2[b];
                b--;
            }
            c--;
        }
        for(;a>=0;a--, c--)
            arr2[c] = arr1[a];
    }