public static List merge(List[] xss, Comparator cmp) {
    	int[] next = new int[xss.length];
    	for (int i=0; i < next.length; i++) {
    		next[i] = 0;
    	}
    	List merged = null;
    	int index = 0;
    	while (true) {
    		index = minIndex(xss, next, cmp);
    		if (index == -1) { break;}
    		merged.add(xss[index].get(next[index]));
        	next[index]++;
    	}
		return merged;
    }