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# Solution 1 by cases

* t-complexity: $O(n)$
* s-complexity: %O(1)%

three cases that will not self crossing:

* always out: dist\[i] > dist\[i-2]
* always in: dist\[i] < dist\[i-2]
* first out then in:

see graph at: <https://leetcode-cn.com/problems/self-crossing/solution/tong-ge-lai-shua-ti-la-san-chong-bu-xian-w80r/>