Error while merging two arrays

Question

I have two sorted arrays arr1 and arr2 and I am trying to merge these two arrays into another array 'output'. But the problem is if the first array gets exhausted ie array arr1 gets completely used then value of 'i' will be more than the length of the array so on next iteration arr[i] gives an error. What can be done to avoid this?

    int i=0;
    int j=0;

    for(int k=0;k<output.length;k++) {      

            if(arr1[i]<arr2[j]) {
                output[k]=arr1[i];
                i++;
            }


            else{           
                   output[k]=arr2[j];
                   j++;         
            }       

    }

Answer 1

You need to check if the arrays are exhausted :

int i=0;
int j=0;

for(int k=0;k<output.length;k++) {      
    if(i < arr1.length && j < arr2.length) { 
        // both arrays still have unused elements
        if (arr1[i]<arr2[j]) {
            output[k]=arr1[i];
            i++;
        } else {           
           output[k]=arr2[j];
           j++;         
        } 
    } else if (i < arr1.length) {
        // only the first array has unused elements
        output[k]=arr1[i];
        i++;   
    } else if (j < arr2.length) {
        // only the second array has unused elements
        output[k]=arr2[j];
        j++; 
    } 
}

Answer 2

We can take advantage of the fact that the value of k does not have to be checked since the output array has its length equal to the sum of lengths of arr1 and arr2. Once either of the arrays has its elements exhausted, we exit from the main for loop( hence the conditions i < arr1.length && j < arr2.length). Now, since one of the arrays has been exhausted, we just need to dump all of the remaining elements of the other array into the output array. Hence we check the condition if i != arr1.length which if true would mean that j is equal to arr2.length therefore arr2 has been exhausted and elements of arr1 have to be dumped into output array. Else, we dump the remaining of the arr2 elements into the output array.

int i=0;
int j=0;

for(int k=0;i<arr1.length && j < arr2.length ;k++) {      

        if(arr1[i]<arr2[j]) {
            output[k]=arr1[i];
            i++;
        }


        else{           
               output[k]=arr2[j];
               j++;         
        }       

}
if(i != arr1.length){
    for(; i < arr1.length; i++,k++)
    output[k]=arr1[i];
}
else{
    for(; j < arr2.length; j++,k++)
    output[k]=arr2[j];
}