Because of the Leftist Property the right path of every element in the heap has the
shortest path to an external node. Therefore the Union Operation has sufficiently
enhanced and runs in O (log n) time.
In some applications, pairs of heaps are repeatedly unioned; spending linear time per
union operation would be out of the question. Leftist Heap supports union in O (log n)
time and therefore is a good candidate for applications that will repeatedly call the Union
operation.