会场安排问题

Descr iption

假设要在足够多的会场里安排一批活动，并希望使用尽可能少的会场。设计一个有效的

贪心算法进行安排。(这个问题实际上是著名的图着色问题。若将每一个活动作为图的一个

顶点，不相容活动间用边相连。使相邻顶点着有不同颜色的最小着色数，相应于要找的最小

会场数。)

编程任务：

对于给定的k个待安排的活动，编程计算使用最少会场的时间表。

Input

由文件input.txt给出输入数据。第一行有1 个正整数k，表示有k个待安排的活动。接

下来的k行中，每行有2个正整数，分别表示k个待安排的活动开始时间和结束时间。时间

以0 点开始的分钟计。

Output

将编程计算出的最少会场数输出到文件output.txt。

Sample Input

5

1 23

12 28

25 35

27 80

36 50

Sample Output

3

-Venue arrangements

Descr iption

Assumed to be a sufficient number of arrangements for a number of activities inside the venue, and hoped to use as little as possible venue. To design an effective

Greedy algorithm to arrange. (This problem is actually well-known graph coloring problem. If we each activity as a graph

Vertex, between incompatible activities connected with the edge. So that adjacent vertices have different colors with minimum chromatic number, corresponding to the minimum to find

Site number. )

Programming tasks:

For a given k were to be arranged activities, calculated using the programming schedule for at least the venue.

Input

Given input data from the file input.txt. The first line has a positive integer k, that there are k-to be arranged activities. Then

K down the line, each line has two positive integers k, respectively, the activities were to be arranged start time and end time. Time

To 0:00 start of the minutes.

Output

Will be programmed to calculate th