HDU 3697 Selecting courses（贪心）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3697

题意：有n门课程(n<=300),每门课程有个选课的时间段s,e,只能在s之后，在e之前选择该门课程。每位同学可以选择任意一个开始时间，然后每5分钟有一次选课机会，问每位同学最多可以选多少门课。

思路：对于一个整数时刻p，p+eps作为开始时刻比p更优，且开区间(p,p+1)内所有时刻作为开始时刻都与p+eps是一样的。将所有区间按照结束时刻升序排序，结束时刻早的先选。

#include <iostream>
#include <cstdio>
#include <string.h>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <map>
#include <ctype.h>
#include <time.h>

#define abs(x) ((x)>=0?(x):-(x))
#define i64 long long
#define u32 unsigned int
#define u64 unsigned long long
#define clr(x,y) memset(x,y,sizeof(x))
#define CLR(x) x.clear()
#define ph(x) push(x)
#define pb(x) push_back(x)
#define Len(x) x.length()
#define SZ(x) x.size()
#define PI acos(-1.0)
#define sqr(x) ((x)*(x))
#define MP(x,y) make_pair(x,y)
#define EPS 1e-15

#define FOR0(i,x) for(i=0;i<x;i++)
#define FOR1(i,x) for(i=1;i<=x;i++)
#define FOR(i,a,b) for(i=a;i<=b;i++)
#define FORL0(i,a) for(i=a;i>=0;i--)
#define FORL1(i,a) for(i=a;i>=1;i--)
#define FORL(i,a,b)for(i=a;i>=b;i--)

#define rush() int CC;for(scanf("%d",&CC);CC--;)
#define Rush(n) while(scanf("%d",&n)!=-1)
using namespace std;

void RD(int &x){scanf("%d",&x);}
void RD(i64 &x){scanf("%I64d",&x);}
void RD(u64 &x){scanf("%I64u",&x);}
void RD(u32 &x){scanf("%u",&x);}
void RD(double &x){scanf("%lf",&x);}
void RD(int &x,int &y){scanf("%d%d",&x,&y);}
void RD(i64 &x,i64 &y){scanf("%I64d%I64d",&x,&y);}
void RD(u32 &x,u32 &y){scanf("%u%u",&x,&y);}
void RD(double &x,double &y){scanf("%lf%lf",&x,&y);}
void RD(double &x,double &y,double &z){scanf("%lf%lf%lf",&x,&y,&z);}
void RD(int &x,int &y,int &z){scanf("%d%d%d",&x,&y,&z);}
void RD(i64 &x,i64 &y,i64 &z){scanf("%I64d%I64d%I64d",&x,&y,&z);}
void RD(u32 &x,u32 &y,u32 &z){scanf("%u%u%u",&x,&y,&z);}
void RD(char &x){x=getchar();}
void RD(char *s){scanf("%s",s);}
void RD(string &s){cin>>s;}

void PR(int x) {printf("%d\n",x);}
void PR(int x,int y) {printf("%d %d\n",x,y);}
void PR(i64 x) {printf("%lld\n",x);}
void PR(i64 x,i64 y) {printf("%I64d %I64d\n",x,y);}
void PR(u32 x) {printf("%u\n",x);}
void PR(u64 x) {printf("%I64u\n",x);}
void PR(double x) {printf("%.6lf\n",x);}
void PR(double x,double y) {printf("%.5lf %.5lf\n",x,y);}
void PR(char x) {printf("%c\n",x);}
void PR(char *x) {printf("%s\n",x);}
void PR(string x) {cout<<x<<endl;}

void upMin(int &x,int y) {if(x>y) x=y;}
void upMin(i64 &x,i64 y) {if(x>y) x=y;}
void upMin(double &x,double y) {if(x>y) x=y;}
void upMax(int &x,int y) {if(x<y) x=y;}
void upMax(i64 &x,i64 y) {if(x<y) x=y;}
void upMax(double &x,double y) {if(x<y) x=y;}

const int mod=10000;
const i64 inf=((i64)1)<<60;
const int INF=1000000000;
const int N=10005;

struct node
{
int L,R;

void get()
{
RD(L,R);
}
};

node a
;
int n;

int cmp(node a,node b)
{
return a.R<b.R;
}

int h
;

int main()
{
Rush(n)
{
if(!n) break;
int i,j,k,temp;
FOR1(i,n) a[i].get();
sort(a+1,a+n+1,cmp);
int ans=0;
FOR0(i,5)
{
clr(h,0); temp=0;
for(j=i;j<=1000;j+=5) for(k=1;k<=n;k++)
{
if(!h[k]&&a[k].L<=j&&j<a[k].R)
{
h[k]=1; temp++;
break;
}
}
upMax(ans,temp);
}
PR(ans);
}
}