[BZOJ1664] [Usaco2006 Open]County Fair Events 参加节日庆祝

[Usaco2006 Open]County Fair Events 参加节日庆祝

Description

Farmer John has returned to the County Fair so he can attend the special events (concerts, rodeos, cooking shows, etc.). He wants to attend as many of the N (1 <= N <= 10,000) special events as he possibly can. He’s rented a bicycle so he can speed from one event to the next in absolutely no time at all (0 time units to go from one event to the next!). Given a list of the events that FJ might wish to attend, with their start times (1 <= T <= 100,000) and their durations (1 <= L <= 100,000), determine the maximum number of events that FJ can attend. FJ never leaves an event early.

有N个节日每个节日有个开始时间,及持续时间. 牛想尽可能多的参加节日,问最多可以参加多少. 注意牛的转移速度是极快的,不花时间.

Input

Line 1: A single integer, N.
Lines 2..N+1: Each line contains two space-separated integers, T and L, that describe an event that FJ might attend.

Output

Line 1: A single integer that is the maximum number of events FJ can attend.

Sample Input

1 6

8 6

14 5

19 2

1 8

18 3

10 6

Sample Output

OUTPUT DETAILS:

FJ can do no better than to attend events 1, 2, 3, and 4.

Source

Silver

题解

贪心，按结束时间排序

var
 a:array[0..10000,1..2]of longint;
 i,j,k:longint;
 n,b,ans:longint;
procedure sort(l,r: longint);
var i,j,x,y: longint;
begin
 i:=l; j:=r; x:=a[(l+r) div 2,2];
repeat
while a[i,2]<x do inc(i);
while x<a[j,2] do dec(j);
if not(i>j) then
begin
    y:=a[i,2]; a[i,2]:=a[j,2]; a[j,2]:=y;
    y:=a[i,1]; a[i,1]:=a[j,1]; a[j,1]:=y;
    inc(i); dec(j);
end;
until i>j;
if l<j then sort(l,j);
if i<r then sort(i,r);
end;

begin
 readln(n);
for i:=1 to n do
begin
   readln(a[i,1],b);
   a[i,2]:=b+a[i,1];
end;
 sort(1,n); ans:=0; b:=0;
for i:=1 to n do
if b<=a[i,1]
then begin inc(ans); b:=a[i,2]; end;
 writeln(ans);
end.

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