Codeforces Round #331 (Div. 2) C. Wilbur and Points
2015-11-17 09:44
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题意:
给你一些点,把他们排好序,要求就是对于任意点(x,y),点(x1,y1) 必须排在后面(x≤x1,y≤y1),而且每个点的y−x 满足给定的序列!思路:
这题做法很多啊,貌似看到有用线段树做的,其实注意到题目给的性质根本就不需要啦,首先根据给定的序列填入对应的点(w[i]相同的话,小的排在前面),中途加一些判断,假设这一部分你已经会了!然后就是判断我们得到的序列是否合法,也就是判断是否满足上面说的那个要求。
关键就是如何判断呢?注意到题目给定的条件:
if some point (x, y) belongs to the set, then all points (x’, y’), such that 0 ≤ x’ ≤ x and 0 ≤ y’ ≤ y also belong to this set.
所以只需把我们得到的序列扫一遍遇到点(x,y),判断下(x−1,y),(x,y−1),(x−1,y−1) 前面是否出现过就好了,这个判断是否出现过,可以用hash啊map啊什么的。原理这个自己好好想想,还是比较简单的!
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