ICPC 2019-2020 North-Western Russia Regional Contest
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Problem A
Solved by Xiejiadong. 00:15 (+)
温暖的模拟题。
Problem B
Solved by Kilo_5723. 02:23 (+)
Problem C
Solved by Kilo_5723. 03:32 (+2)
Problem D
Unsolved.
Problem E
Solved by Xiejiadong. 02:39 (+2)
题意:在树上求一个点,使得其到所有特殊点距离相等。
题解:对于所有的特殊点按照顺序,使得相邻的两个距离都相等即可。
对于能使两个点距离相等的,首先求两个点距离的中点(长度为偶数,没有中点,一定无解)。
而所有满足要求的点,一定是中点连出去的所有链,去掉两个点所在的那条链,相当于是一个子树去掉一部分子子树。
按照 dfs 标号以后,子树的问题就可以变成区间问题,用线段树维护标记,每次操作修改一些标记。
最后查询是否存在满足要求的标记就好了。
链的中点,可以通过倍增 lca 来完成。
Problem F
Unsolved.
Problem G
Unsolved.
Problem H
Solved by Weaver_zhu. 01:07 (+)
Problem I
Solved by Kilo_5723. 01:46 (+)
Problem J
Solved by Weaver_zhu. 02:12 (+)
Problem K
Upsolved by Weaver_zhu. (-2)
Problem L
Unsolved.
Problem M
Solved by Kilo_5723. 01:11 (+3)