algs4partI-004: 8puzzle WIP

Compilation:  PASSED
Style:        PASSED
Findbugs:     No potential bugs found.
API:          PASSED

Correctness:  24/25 tests passed
Memory:       8/8 tests passed
Timing:       17/17 tests passed

Raw score: 97.40% [Correctness: 65%, Memory: 10%, Timing: 25%, Style: 0%]