before sorting : 29 -> 4 -> 17 -> 4 -> 42 -> 8 -> 15 -> NULL
after sorting  : 4 -> 4 -> 8 -> 15 -> 17 -> 29 -> 42 -> NULL
after insert   : 4 -> 4 -> 8 -> 15 -> 17 -> 29 -> 42 -> 23 -> NULL
passes: 4, swaps: 10
