P1. Construct the tree with post-order traversal string = i b d
a h g c f, and in-order traversal string = b i a d f g h c.
P2. Construct the tree with pre-order traversal string = 10, 20,
40, 50, 80, 60, 70, 90, and in-order traversal string = 40, 50, 20,
10, 80, 70, 90, 60.