[Violet]蒲公英 分块

Code:

#include<cstdio>
#include<string>
#include<iostream>
#include<algorithm>
#include<vector>
#include<cstring>
#include<cmath>
using namespace std;
void setIO(string a){ freopen((a+".in").c_str(),"r",stdin); }

const int maxn=40000+5;
int n,m,block;
int col[maxn],A[maxn],belong[maxn],bucket[maxn];
int prefix[300][maxn];                   
int best[300][300];                    
vector<int>position[maxn],solve;
int st(int i){ return (i-1)*block+1; }   
int ed(int i){ return min(i*block,n);}   
int main(){
	//setIO("input");
	scanf("%d%d",&n,&m);
	block=sqrt(n);
	for(int i=1;i<=n;++i) {
		scanf("%d",&col[i]);
		A[i]=col[i];
		belong[i]=(i-1)/block+1;
	}
	sort(A+1,A+1+n);
    for(int i=1;i<=n;++i) {
    	col[i]=lower_bound(A+1,A+1+n,col[i])-A;
    	prefix[belong[i]][col[i]]+=1;
    }
    for(int i=1;i<=belong[n];++i)
    	for(int j=1;j<=n;++j) prefix[i][j]+=prefix[i-1][j];

    for(int length=1;length<=belong[n];++length)
    	for(int i=1;i+length-1<=belong[n];++i)
    	{
    		int j=i+length-1;
    		int tmp=0,cur=0;
     		for(int k=st(i);k<=ed(i);++k)          //枚举 i 中颜色
     		{        
    			int delta=prefix[j][col[k]]-prefix[i-1][col[k]];   
    			if(delta >= tmp){
    				if(delta>tmp) tmp=delta,cur=col[k];
    				else if(col[k]<cur) cur=col[k];
    			}
    		}
    		for(int k=st(j);k<=ed(j);++k){         //枚举 j 中颜色
    			int delta=prefix[j][col[k]]-prefix[i-1][col[k]];
    			if(delta >= tmp){
    				if(delta>tmp) tmp=delta,cur=col[k];
    				else if(col[k]<cur) cur=col[k];
    			}
    		}
    	
    		if(j>i){
    			int delta;
    			delta=prefix[j][best[i+1][j]]-prefix[i-1][best[i+1][j]];
    			if(delta>=tmp){
    				if(delta>tmp) tmp=delta, cur=best[i+1][j];
    				else if(best[i+1][j]<cur) cur=best[i+1][j];
    			}

    			delta=prefix[j][best[i][j-1]]-prefix[i-1][best[i][j-1]];
    			if(delta>=tmp){
    				if(delta>tmp) tmp=delta, cur=best[i][j-1];
    				else if(best[i][j-1]<cur) cur=best[i][j-1];
    			}
    		}
    		best[i][j]=cur;
    	}
    int lastans=0,l,r;
    while(m--){
    	scanf("%d%d",&l,&r);
    	l=(l+lastans-1)%n+1;
    	r=(r+lastans-1)%n+1;
    	if(l>r) swap(l,r);
    	for(int i=l;i<=min(ed(belong[l]),r);++i) {
    		bucket[col[i]]+=1; 
    		solve.push_back(col[i]);
    	}
    	if(belong[l] != belong[r]){
    		for(int i=st(belong[r]);i<=r;++i) {
    			bucket[col[i]]+=1; 
    			solve.push_back(col[i]);
    		}
    	}
    	int tmp=0,cur=0;
    	int blockl=belong[l]+1, blockr=belong[r]-1;
    	if(blockl<=blockr){
    		cur=best[blockl][blockr], tmp=prefix[blockr][cur]-prefix[blockl-1][cur];
    		for(int i=0;i<solve.size();++i){
    			int delta=prefix[blockr][solve[i]]-prefix[blockl-1][solve[i]]+bucket[solve[i]];
    			if(delta>=tmp){
    				if(delta>tmp) tmp=delta,cur=solve[i];
    				else if(solve[i]<cur) cur=solve[i];
    			}
    		}
    	}   
    	else{
    		for(int i=0;i<solve.size();++i){
    			int delta=bucket[solve[i]];
    			if(delta>=tmp){
    				if(delta>tmp) tmp=delta, cur=solve[i];
    				else if(solve[i]<cur) cur=solve[i];
    			}
    		}
    	}	
    	for(int i=0;i<solve.size();++i) bucket[solve[i]]=0;
    	solve.clear();
    	lastans=A[cur];
    	printf("%d\n",lastans);
    }
    return 0;
}