public static void main(String args[]){
        int input1[] = {1};
        int input2[] = {4,2};
        int input3[] = {6,2,9};
        int input4[] = {6,-1,10,4,11,14,19,12,18};
        MergeSort ms = new MergeSort();
        ms.sort(input1);
        ms.sort(input2);
        ms.sort(input3);
        ms.sort(input4);
        
        ms.printArray(input1);
        ms.printArray(input2);
        ms.printArray(input3);
        ms.printArray(input4);
    }
http://en.wikipedia.org/wiki/Merge_sort
Test cases
1 element
2 element
negative numbers
already sorted
reverse sorted
src/com/interview/sort/MergeSort.java