Figure 2.

Pseudo codes of combo score functions: combo1 and combo2. (a) combo1: a score function that considers nodes with one vertical grid distance from the target node. (b) combo2: a score function that considers nodes with up to two vertical grid distances from the target node, (c) isCombo: a boolean function that takes a node and a grid point as its arguments and returns "true" if the attribute of the node and that of the node on the grid point are the same.