I finally managed to breach the 100 sec barrier of Minesweeper-Expert field yesterday night.
3BV of the entire minefield above = 136 + 12 = 148
3BV measure (abbreviated from Bechtel's Board Benchmark Value) is the measure of difficulty of a minesweeper field.
3BV/sec = 148/(98-1) = 1.526
Flagging style was used to mark the mines.
But I still regret the missed chance of sweeping the field within 91 secs due to Mine probability problem for the last mine, just a few minutes before I finished this one.
