二分答案+哈希（奇怪的思路）

代码

#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,m,a[1000002],MAX=-1,MIN=0x7f7f7f7f,l,r,mid,ans=0x7f7f7f7f;
unordered_map<int,int> tp;
bool check(){
	cout<<mid<<"mid\n";
	for(int i=MIN;i<=MAX;i++){
		if(tp[i]>=m) return true;
		else{
			int cnt=m;
			cnt-=tp[i];
			int flj=0,flk=0;
			cout<<"kt "<<i<<endl;
			for(int j=i+1,k=i-1;(j-k)<=mid;){
				cout<<j<<' '<<k<<" c "<<cnt<<endl;
				if(cnt<=0) return true;
				if(j<=n&&flj==0){
					if(tp[j]!=0) cnt-=tp[j];
					j++;
				}
				else if(flj==0){
					flj=1;
					j--;
				}
				if((j-k)==mid){
					if(cnt<=0) return true;
					else if(flk==0){
						cout<<j<<" "<<k<<" "<<cnt<<" "<<tp[j]<<" ff "<<tp[k]<<endl;
						cnt+=tp[j];
						cout<<"cnttttttt "<<cnt<<endl;
						cnt-=tp[k];
						if(cnt<=0){
							cout<<111111<<endl;
							return true;
						}
						else break;
					}
				}
				if(k>=1&&flk==0){
					if(tp[k]!=0) cnt-=tp[k];
					k--;
				}
				else if(flk==0){
					flk=1;
					k++;
				}
				cout<<j<<' '<<k<<" "<<cnt<<endl;
			}
		}
	}
	return false;
}
signed main(){
	//freopen("ring3.in","r",stdin);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		MAX=max(MAX,a[i]);
		MIN=min(MIN,a[i]);
		tp[a[i]]++;
	} 
	l=0,r=MAX-MIN;
	while(l<r){
		mid=(l+r)/2;
		if(check()){
			ans=min(ans,mid);
			r--;
		}
		else l++;
	}
	cout<<ans;
	return 0;
}