Determine the optimal way of specifying subfigure labels

[wojtask]

Subfigure labels ((a), (b), etc.) can be placed under or to the left of a subfigure, depending on a case. Find an optimal way of specifying them - using the subcaption package together with \captionsetup config, or using TikZ to add labels directly in the picture. In the latter we can have more flexibility in terms of specifying positions or aligning the labels to specific objects in the picture.

[wojtask]

Sometimes, label is not needed precisely at the middle of the figure box. For instance, in some figures involving unbalanced trees (see Chapter 6) it's better to place the label that is aligned to the root of the tree, which is not necessarily precisely in the middle.