#1651. [Usaco2006 Feb]Stall Reservations 专用牛棚

题目描述

Oh those picky N (1 <= N <= 50,000) cows! They are so picky that each one will only be milked over some precise time interval A..B (1 <= A <= B <= 1,000,000), which includes both times A and B. Obviously, FJ must create a reservation system to determine which stall each cow can be assigned for her milking time. Of course, no cow will share such a private moment with other cows. Help FJ by determining: * The minimum number of stalls required in the barn so that each cow can have her private milking period * An assignment of cows to these stalls over time

有N头牛,每头牛有个喝水时间,这段时间它将专用一个Stall 现在给出每头牛的喝水时间段,问至少要多少个Stall才能满足它们的要求

输入格式

• Line 1: A single integer, N

• Lines 2..N+1: Line i+1 describes cow i's milking interval with two space-separated integers.

输出格式

• Line 1: The minimum number of stalls the barn must have.

• Lines 2..N+1: Line i+1 describes the stall to which cow i will be assigned for her milking period.

样例

样例输入

5  

1 10  

2 4  

3 6  

5 8  

4 7  

样例输出

4  

  

  

OUTPUT DETAILS:  

  

Here's a graphical schedule for this output:  

  

Time     1  2  3  4  5  6  7  8  9 10  

Stall 1 c1>>>>>>>>>>>>>>>>>>>>>>>>>>>  

Stall 2 .. c2>>>>>> c4>>>>>>>>> .. ..  

Stall 3 .. .. c3>>>>>>>>> .. .. .. ..  

Stall 4 .. .. .. c5>>>>>>>>> .. .. ..  

  

Other outputs using the same number of stalls are possible.

数据范围与提示

不妨试下这个数据,对于按结束点SORT,再GREEDY的做法 1 3 5 7 6 9 10 11 8 12 4 13 正确的输出应该是3