BZOJ 4582: [Usaco2016 Open]Diamond Collector

/**************************************************************
    Problem: 4582
    User: BeiYu
    Language: C++
    Result: Accepted
    Time:76 ms
    Memory:1876 kb
****************************************************************/
 
#include <cstdio>
#include <algorithm>
#include <iostream>
using namespace std;
 
const int N =50050;
 
int n,k,ans;
int a[N];
int f[N],g[N];
 
inline int in(int x=0){ scanf("%d",&x);return x; }
int uppp(int x){// >=
    int l=1,r=n,mid;
    for(;l<=r;){
        mid=(l+r)>>1;
        if(a[mid] < x) l=mid+1;
        else r=mid-1;
    }return l;
}
int lwww(int x){//<=
    int l=1,r=n,mid;
    for(;l<=r;){
        mid=(l+r)>>1;
        if(a[mid] <= x) l=mid+1;
        else r=mid-1;
    }return r;
}
int main(){
    n=in(),k=in();
    for(int i=1;i<=n;i++) a[i]=in();
    sort(a+1,a+n+1);
     
     
    for(int i=1;i<=n;i++){
        f[i]=i-uppp(a[i]-k)+1;
        g[i]=lwww(a[i]+k)-i+1;
    }
     
//  for(int i=1;i<=n;i++) cout<<a[i]<<" ";cout<<endl;
//  for(int i=1;i<=n;i++) cout<<f[i]<<" ";cout<<endl;
//  for(int i=1;i<=n;i++) cout<<g[i]<<" ";cout<<endl;
     
    for(int i=1;i<=n;i++){
        ans=max(ans,f[i-1]+g[i]);
        f[i]=max(f[i],f[i-1]);
    }
    cout<<ans<<endl;
    return 0;
}