merging_sort.js

/*
A = array(1, 3, 5, null, null, null);
B = array(2, 4, 6);


merge_sort(A, B);

console.log(B)
>> (1,2,3,4,5,6)
*/

/* left array is big enough for results, scan both arrays and leave result sorted, empty elements are null */
function merge_sort(A, B) {

    var i = A.length - 1;
    var j = B.length - 1;
    var pos = A.length - 1;

    while (i > 0 || j > 0) {
        if (A[i] != null) {
            if (j < 0 || A[i] >= B[j])  {
                A[pos] = A[i];
                i--;
            } else if (i < 0 || B[j] > A[i]) {
                A[pos] = B[j];
                j--;
            }
            pos--;
        } else {
            i--;
        }
    }
}