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3109：Inner Vertices
题目描述
There is an infinite square grid. Some vertices of the grid are black and other vertices are white.
A vertex V is called inner if it is both vertical-inner and horizontal-inner. A vertex V is called horizontal-inner if there are two such black vertices in the same row that V is located between them. A vertex V is called vertical-inner if there are two such black vertices in the same column that V is located between them.
On each step all white inner vertices became black while the other vertices preserve their colors. The process stops when all the inner vertices are black.
Write a program that calculates a number of black vertices after the process stops.
输入解释
The first line of the input file contains one integer number n (0 ≤ n ≤ 100 000) — number of black vertices at the beginning.
The following n lines contain two integer numbers each — the coordinates of different black vertices. The coordinates do not exceed 109 by their absolute values.
输出解释
Output the number of black vertices when the process stops. If the process does not stop, output -1.
输入样例
4 0 2 2 0 -2 0 0 -2
输出样例
5
提示
来自北京大学POJ的附加信息
| Case time limit(单组数据时间限制) | 2000MS |
最后修改于 2020-10-29T06:52:55+00:00 由爬虫自动更新
共提交 0 次
通过率 --%
| 时间上限 | 内存上限 |
| 5000 | 65536 |