P3143 [USACO16OPEN]Diamond Collector S

Lisa

首先强行选择一个点

然后计算它左边最多长区间，右边也是

就可以了

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;
int a[600001];
int n,k;
int l[600001];
int ans;
int main(){
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;++i){
		scanf("%d",&a[i]);
	}
	sort(a+1,a+n+1);
	a[n+1]=9999999999;
	for(int i=1;i<=n;++i){
		int ll=lower_bound(a+1,a+i+1,a[i]-k)-a;
		l[i]=max(l[i-1],i-ll+1);
	//	cout<<l[i]<<endl;
	}
	for(int i=n-1;i>=1;--i){
		int rr=upper_bound(a+1+i,a+n+1,a[i+1]+k)-a;
		if(a[rr]>a[i+1]+k){
			rr--;
		} 
		ans=max(ans,l[i]+(rr-i));
	}
	cout<<ans;
	return 0;
}