SEARCH(10)  path: 20 -> 8 -> 12 -> 10   (4 nodes visited)
SEARCH(13)  path: 20 -> 8 -> 12 -> 14   (4 nodes visited)
MINIMUM     path: 20 -> 8 -> 4   (3 nodes visited)
MAXIMUM     path: 20 -> 22   (2 nodes visited)

key 8: successor = 10, predecessor = 4
key 10: successor = 12, predecessor = 8
key 14: successor = 20, predecessor = 12
key 4: successor = 8, predecessor = none
key 22: successor = none, predecessor = 20
