这个条件如第35行所示，其中，如果在一段连续的时间内对该列排序，并且以前的排序方向为升序，那么它必须切换为降序排序。
This condition is shown in line 35, where if the column is being sorted for a consecutive time and the previous direction was upward, it must be switched to downward sorting.
行代表的是问题的影响，严重程度从下至上升序排列。
The rows represent the impact of a problem, increasing in severity from the bottom to the top.
对于其他任何情况，树必须按升序排序(第75 - 116行)。
For any other case, the tree must be sorted upward (lines 75 to 116).
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