BZOJ 1828 农场分配（贪心）

题目链接：http://61.187.179.132/JudgeOnline/problem.php?id=1828

题意：



思路：将区间按照右端点升序排序，右端点相同的左端点大的在前面。然后一个一个选，用线段树维护区间最小值。

#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-6

#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("%lld",&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("%lld%lld",&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("%lld%lld%lld",&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("%lld %lld\n",x,y);}
void PR(u32 x) {printf("%u\n",x);}
void PR(u64 x) {printf("%llu\n",x);}
void PR(double x) {printf("%.2lf\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=1000000007;
const i64 inf=((i64)1)<<60;
const double dinf=1000000000000000000.0;
const int INF=1000000;
const int N=100005;

struct node
{
int L,R;

int operator<(const node &a) const
{
if(R!=a.R) return R<a.R;
return L>a.L;
}
};

node b
;
int n;

struct Node
{
int L,R,Min,det;

void sub(int x)
{
det+=x;
Min-=x;
}
};

Node a[N<<2];

void pushUp(int t)
{
if(a[t].L==a[t].R) return;
a[t].Min=min(a[t*2].Min,a[t*2+1].Min);
}

int d
;

void build(int t,int L,int R)
{
a[t].L=L;
a[t].R=R;
a[t].det=0;
if(L==R)
{
a[t].Min=d[L];
return;
}
int mid=(L+R)>>1;
build(t*2,L,mid);
build(t*2+1,mid+1,R);
pushUp(t);
}

void pushDown(int t)
{
if(a[t].L==a[t].R) return;
if(a[t].det)
{
a[t*2].sub(a[t].det);
a[t*2+1].sub(a[t].det);
a[t].det=0;
}
}

void add(int t,int L,int R)
{
if(L>a[t].R||R<a[t].L) return;

if(L<=a[t].L&&a[t].R<=R)
{
a[t].det++;
a[t].Min--;
return;
}

pushDown(t);
add(t*2,L,R);
add(t*2+1,L,R);
pushUp(t);
}

int query(int t,int L,int R)
{
if(L>a[t].R||R<a[t].L) return INF;
if(L<=a[t].L&&a[t].R<=R) return a[t].Min;

pushDown(t);

int ans=min(query(t*2,L,R),query(t*2+1,L,R));
pushUp(t);
return ans;
}

int m;

int main()
{
RD(n,m);
int i;
FOR1(i,n) RD(d[i]);
build(1,1,n);
FOR0(i,m) RD(b[i].L,b[i].R);
sort(b,b+m);
int ans=0;
FOR0(i,m)
{
if(query(1,b[i].L,b[i].R)>=1)
{
ans++;
add(1,b[i].L,b[i].R);
}
}
PR(ans);
}