If the A* calculation for a shortcut (in Step 3) finds it's now impassable, or if its actual detailed cost is significantly different (e.g., 20%) from the pre-calculated shortcut value:
按照过往的互联网运营思维来看，这当然谈不上是什么成功的拉新活动。各家的钱都没少烧，ROI却不见起色，用户薅完羊毛心满意足地转身离去，产品还是没多少人主动用。
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I started this way to isolate the hardest part of the problem - turn detection - without wiring up the rest of the system.