I have to Arrays, each represents a list of Stories. Two users can concurrently modify the order, add or remove Stories, and I want those changes merged.

An example should make this clearer

Orignial       1,2,3,4,5
UserA (mine)   3,1,2,4,5 (moved story 3 to start)
UserB (theirs) 1,2,3,5,4 (moved story 5 forward)

The result of the above should be

Merge (result) 3,1,2,5,4

In case of conflicts, UserA should always win.

I came pretty far with this simple approach. First i deleted whatever mine says i should deleted (that part of the code is not shown, it's trivial), then I iterate of mine, inserting and moving from theirs what is needed (mstories = mine, tstories = theirs):

     var offset = 0;
     for (var idx=0;idx<mstories.length;idx++) {
        var storyId = mstories[idx];

        // new story in theirs
        if (mstories.indexOf(tstories[idx]) == -1) {
           mstories.splice(idx+1, 0, tstories[idx]);
           idx--;
           continue;
        }
        // new story in mine?
        if (tstories.indexOf(storyId) == -1) {
           tstories.splice(idx+offset, 0, storyId);
           offset += 1;
        // story moved
        } else if (tstories.indexOf(storyId) != idx + offset) {
           tstories.splice(tstories.indexOf(storyId), 1);
           tstories.splice(idx+offset, 0, storyId);
        }
     }

It's close, but it gets confused when too many Stories are moved to the front / back with Stories in between, which the other User touched.

I have an extended version which does checks on the original and is smarter - holding 2 offsets, etc - , but I feel like this is a problem that must have a) a name b) a perfect solution and i don't want to re-invent it.