Obtain the optimal binary search tree with equal probabilities for the identifier set (a₁, a₂, a₃) = ( if, stop, while)

Minimum number of comparisons required to sort 5 elements

The following sequence of operations is performed on stack: PUSH (10),PUSH (20),POP,PUSH (10),PUSH (20),POP,POP,POP,PUSH (20),POP The sequence of the value popped out is:

If the binary tree in figure is traversed in inorder, then the order in which the nodes will be visited is ______