[USACO14JAN]记录奥林比克

题目描述
Being a fan of all cold-weather sports (especially those involving cows),Farmer John wants to record as much of the upcoming winter Moolympics as possible.
The television schedule for the Moolympics consists of N different programs(1 <= N <= 150), each with a designated starting time and ending time. FJ has a dual-tuner recorder that can record two programs simultaneously.
Please help him determine the maximum number of programs he can record in total.

农民约翰热衷于所有寒冷天气的运动（尤其是涉及到牛的运动）， 农民约翰想记录尽可能多的moolympics为即将到来的冬季 可能的。 为moolympics电视时间表由N个不同的程序 （1 < = n＝150），每个具有指定的开始时间和结束时间。FJ 有一个双调谐器录音机，可以同时录制两个节目。 请帮助他确定他能录制的节目的最大数量。

输入输出格式

输入格式：
* Line 1: The integer N.
* Lines 2..1+N: Each line contains the start and end time of a single program (integers in the range 0..1,000,000,000).
第1行：整数n。 第2行.. 1 + n：每行包含单个的开始和结束时间 程序（范围为0…1000000000的整数）。

输出格式：
* Line 1: The maximum number of programs FJ can record.
仅一行，节目FJ可以记录的最大数量。

输入输出样例

输入样例#1：
6
0 3
6 7
3 10
1 5
2 8
1 9
输出样例#1：
4

说明
INPUT DETAILS:
The Moolympics broadcast consists of 6 programs. The first runs from time 0 to time 3, and so on.
OUTPUT DETAILS:
FJ can record at most 4 programs. For example, he can record programs 1 and 3 back-to-back on the first tuner, and programs 2 and 4 on the second tuner.
Source: USACO 2014 January Contest, Silver
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分析

用贪心。
按照结束时间排序。
若节目可以放.则必定放。
尽量放在结束时间长的1组。
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程序：

var
a,b:array[0..151] of longint;
i,j,n,t,t1,s:longint;
begin
    readln(n);
    for i:=1 to n do
    readln(a[i],b[i]);
    for i:=1 to n-1 do
    for j:=i+1 to n do
    if (b[i]>b[j]) or (b[i]=b[j]) and (a[i]>a[j]) then
    begin
        t:=b[i];b[i]:=b[j];b[j]:=t;
        t:=a[i];a[i]:=a[j];a[j]:=t;
    end;
    t:=0;
    t1:=0;
    s:=0;
    for i:=1 to n do
    if a[i]>=t then
    begin
        inc(s);
        if (t1>=t)and(a[i]>=t1) then t1:=b[i] else t:=b[i];
    end else
    if a[i]>=t1 then
    begin
        inc(s);
        t1:=b[i];
    end;
    writeln(s);
end.