Check subsegments in Fast.java.

Submition Result:

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

Correctness:  36/36 tests passed
Memory:       1/1 tests passed
Timing:       17/17 tests passed

Raw score: 100.00% [Correctness: 65%, Memory: 10%, Timing: 25%, Style: 0%]