耗时可以分为走路的时间和等待的时间。走路的时间可以直接计算。
等待的时间又可以分为第一步等待的时间和两步之间等待的时间。第一步等待就是 $s_i=0$。因为走一步就会切换，所以两步之间需要等待也就是 $s_i=s_{i+1}$。枚举这些位置然后计算经过它的 $(p,q)$ 对数求和即可。
时间复杂度 $O(n)$。
QOJ.ac
QOJ
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Discussion #296 for Problem #7109. Traveling on the Axis
Type: Editorial
Status: Open
Posted by: jiangly
Posted at: 2025-12-14 06:54:55
Last updated: 2025-12-14 06:54:59
题解
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